Friday, 15 September 2017

Aristotle’s errors

How many teeth did Bertrand Russell have? Did Galileo float in water?
Ἔχουσι δὲ πλείους οἱ ἄρρενες τῶν θηλειῶν ὀδόντας καὶ ἐν ἀνθρώποις καὶ ἐπὶ προβάτων καὶ αἰγῶν καὶ ὑῶν· ἐπὶ δὲ τῶν ἄλλων οὐ τεθεώρηταί πω.

Males have more teeth than females, in the cases of humans, sheep, goats, and pigs. In other species an observation has not yet been made.
-- Aristotle, History of animals 501b (2.3.13)
Aristotle sometimes gets a rep nowadays as a pretentious idiot: The Scientist Who Got Everything Wrong. Sometimes even Aristotle’s fans think this --
[Bertrand] Russell provides a concise summary of the thoughts of both [Plato and Aristotle], as well as painting a picture as to why they are so important, despite being wrong about almost everything.
This from a fan of Aristotle! And Bertrand Russell loathed Aristotle:
Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives’ mouths. He said also that children will be healthier if conceived when the wind is in the north. One gathers that the two Mrs Aristotles both had to run out and look at the weathercock every evening before going to bed. He states that a man bitten by a mad dog will not go mad, but any other animal will (Hist. An., 704a); that the bite of the shrewmouse is dangerous to horses, especially if the mouse is pregnant (ibid., 604b); that elephants suffering from insomnia can be cured by rubbing their shoulders with salt, olive-oil, and warm water (ibid., 605a); and so on and so on. Nevertheless, classical dons, who have never observed any animal except the cat and the dog, continue to praise Aristotle for his fidelity to observation.
-- Bertrand Russell, The Impact of Science on Society (2016) pp. 6-7 (orig. publ. 1952)
The trouble with attacking the entire oeuvre of a scholar and scientist in this way is that the examples are very, very cherry-picked. These five blunders are taken from a span of over 400 pages of tiny print full of literally thousands of observations about the animal world. Do we take Russell on faith that they’re representative?

No, we don’t. And I’m not going to let that ‘and so on and so on’ pass. If you want to show that Aristotle was wrong about almost everything, show that he was wrong about almost everything. ‘And so on’ is lazy if you can’t back it up. Russell couldn’t.

Russell’s first criticism, about women’s teeth, is the one that gets the most traction. That must be because it’s the easiest one to correct. Testing the claim about conception during a north wind would require an enormous amount of coordination and many years of research; no one is going to try out the effects of rabies on humans; I defy anyone to get a shrew to bite a horse on command; and elephants were not exactly an everyday sight in ancient Greece.

In fact some of them don’t even necessarily look like blunders, if you approach them in the right way. Seasonal winds are a thing: in Greece, a north wind at conception will often correspond to a birthday between mid-February and the summer solstice. And the time of year of a birthday can correlate very strongly with a child’s success under some circumstances. Aristotle didn’t know why that was, but he did know something about astrology, a field which was not considered ridiculous in his day, and which made similar kinds of predictions. And the behavioural effects of rabies are unquestionably different in animals that can talk and communicate their distress (humans) and those that cannot (every other species). I won’t venture to defend Aristotle on shrew bites and elephant massages.

And then there’s the teeth thing. Aristotle doesn’t use it as a way of showing that women are inferior to men, contrary to what is often claimed -- but it does look ridiculous.

Aristotle on teeth

Did Bertrand Russell count the teeth of any of his wives?

Robin Herbert poses this question in an eloquent defence of Aristotle written in 2014. I certainly haven’t ever counted anyone else’s teeth. I only even counted my own when I was about 10 and was wondering how my adult teeth were coming on. Aristotle, Russell, Herbert, and myself -- we all rely on other people to do that for us.

It may still be fairly argued that women’s teeth is one observation that Aristotle really should have done for himself. I think that’s fair. But only on one condition: you’re only allowed to make that argument if you first go and count the teeth of someone of the opposite sex. After all, you’re the one claiming it’s easy to check ...

Herbert’s defence of Aristotle focuses on rejecting the false idea that Aristotle put his own preconceptions ahead of any observations.
Of course Aristotle is wrong, but he is wrong because he was misinformed about the observation, not — as Russell and de Bono suggest, because he did not believe that observations were important.
With that in mind, let’s do a fact-check of all of Aristotle’s claims about teeth in History of Animals book 2 chapter 3. We don’t want to cherry-pick, do we?
  1. All mammals have teeth -- TRUE
  2. Camels have no teeth in the upper jaw -- FALSE
  3. Some species have tusks, e.g. boars -- TRUE
  4. Some species have pointed teeth, e.g. lions, panthers, and dogs; in such cases, the teeth on either jaw fit into each other -- TRUE
  5. No animal has both tusks and horns -- TRUE as far as I can find out
  6. In general front teeth are cutting teeth, hind teeth are molars -- TRUE
  7. There are exceptions: seals have only cutting teeth -- TRUE
  8. No mammals have a double row of teeth -- TRUE as far as I can find out (apart from anomalous situations, e.g. when a child’s milk teeth don’t fall out until after the permanent teeth have come through)
  9. Doubt cast on Ctesias’ claim of a species called ‘martichora’ that has three rows of teeth -- TRUE that Ctesias’ claim is nonsense
  10. Some species shed their teeth, including humans, horses, mules, and asses -- TRUE
  11. But no species sheds molars -- FALSE
  12. Doubt expressed over reports that some species shed only canines -- TRUE that caution warranted, because the report is inaccurate
  13. Older dogs have blunter teeth -- TRUE
  14. Most animals’ teeth darken as they age; horses are an exception, as their teeth whiten with age -- TRUE observation, but FALSE interpretation in the case of horses: horses’ permanent teeth gradually emerge from the gums and wear down at the tips, over a period of many years, meaning that there will be less discolouration
  15. Canines, between the cutting teeth and molars, are wide at the base but sharp at the tip -- TRUE
  16. Males have more teeth than females in humans, sheep, goats, and pigs -- FALSE
  17. Humans with more teeth tend to be longer-lived; humans with gaps between teeth tend to be shorter-lived -- probably TRUE (edit: because of the economic implications of having good/bad teeth, if nothing else)
  18. Wisdom teeth appear around the age of 20; but sometimes at an advanced age, in which case they are very painful -- TRUE (I haven’t been able to confirm/reject Aristotle’s claim about wisdom teeth erupting as late as age 80, but it is true that problems with wisdom teeth increase significantly with age)
  19. Elephants have four molars on each side -- TRUE
  20. Elephants have two tusks: large and turned upwards in the case of males, small and bent downwards in the case of females -- mostly TRUE: female elephants’ tusks do curve upwards, like males’, but often will be too short to have a significant curve
  21. Elephants have teeth at birth -- TRUE
I’ll score TRUEs as 1. Number 14 gets 0.75: the observations are all accurate, but the interpretation is only half accurate. Number 20 gets 0.75 as well, since female elephants’ tusks curve upwards.

So Aristotle on teeth gets a score of 17.5 out of 21, or 83.3% correct. In my university’s marking schedule, that would get him a grade of A-. Certainly not perfect. But it could be much much worse.

The usual accusation cast at Aristotle is that he put theory, logic, and his own preconceptions ahead of any empirical evidence. Do you seen any sign of that in the list of his claims about teeth? I sure don’t. I see a whole bunch of second-hand reports of empirical observation: most accurate, some inaccurate. I don’t see any trace of a priore assumptions.

Aristotle on gravity

Robin Herbert’s essay brings up another common accusation against Aristotle: that, according to Aristotle, heavier things fall faster than light things. Many modern scientists will put it even less generously: the historian Herbert Butterfield claimed that
Aristotle’s argument [was] that the falling body moved more jubilantly every moment because it found itself nearer home.
-- and many eminent scientists, like B. F. Skinner and Stephen Hawking, have taken this claim on faith even though it is the most bald-faced lie.

Now, it is true that Aristotle probably believed that heavier bodies fall faster than light bodies. And it is certainly true that he was interpreted that way throughout the Mediaeval period and Renaissance, until Galileo’s famous experiments. But once again, Aristotle’s problem isn’t a result of letting a priore assumptions take precedence over empirical evidence: the problem is one of confusion.

The confusion is between gravity and buoyancy. Because in buoyancy, things absolutely do accelerate differently depending on their density.

The context of Aristotle’s claims about heavy and light bodies accelerating differently, in On the sky 308a-b (4.1-2), makes it crystal clear that he is really talking about buoyancy, without realising it.
Language recognizes (a) an absolute, (b) a relative heavy and light. ... Our predecessors have not dealt at all with the absolute use of the terms, but only with the relative. I mean, they do not explain what the heavy is or what the light is, but only the relative heaviness and lightness of things possessing weight. ... By absolutely light, then, we mean that which moves upward or to the extremity, and by absolutely heavy that which moves downward or to the centre. By light or relatively light we mean that one, of two bodies endowed with weight and equal in bulk, which is exceeded by the other in the speed of its downward movement. Those of our predecessors who have entered upon this inquiry have for the most part spoken of light and heavy things only in the sense in which one of two things both endowed with weight is said to be the lighter.
-- Aristotle, On the sky 308a7-308b2, trans. J. L. Stocks
(My underlinings.) You see how the confusion arises? He believes some things like flames are ‘absolutely light’ because apparently they always go up; and he’s wrong about that, because fire is buoyant in air, not because it’s ‘absolutely light’. He hasn’t understood that light : heavy is something different from buoyant : unbuoyant. His definition of heaviness relates to buoyancy, not weight: ‘that one, of two bodies endowed with weight and equal in bulk, which is exceeded by the other in the speed of its downward movement’. This is an exact description of a relatively dense body, that is to say, an unbuoyant body.

So, once again, his problem isn’t that he hates empirical evidence. On the contrary: he has a good grasp of how buoyancy works in practice. It’s that he doesn’t realise that there are situations where even a maximally buoyant object, like a flame, won’t move upwards -- namely, in a vacuum.

If he had lived a century later, and had a chat with Archimedes (whose discovery of the Archimedes principle was more explicitly about buoyancy), Aristotle might well have worked it out. Unfortunately, he didn’t. Archimedes didn’t connect the dots, though he could have. Nor did any of Aristotle’s mediaeval followers. Instead, we had to wait for Galileo, who wasn’t interested in the context of Aristotle’s original claim. Because in context, the underlying idea was dead right: Aristotle’s mistake was in generalising from it.

In fact, it’s hard to believe Galileo even read the Aristotle passage I quoted above.
Salv. ... I greatly doubt that Aristotle ever tested by experiment whether it be true that two stones, one weighing ten times as much as the other, if allowed to fall, would so differ in speed that when the heavier had reached the ground, the other would not have fallen more than 10 cubits.

Simp. His language would seem to indicate that he had tried the experiment, because he says: We see the heavier; now the word see shows that he had made the experiment.

Sagr. But I, Simplicio, who have made the test can assure you that a cannon ball weighing one or two hundred pounds, or even more, will not reach the ground by as much as a span ahead of a musket ball weighing only half a pound, provided both are dropped from a height of 200 cubits.

Salv. But even without further experiment, it is possible to prove clearly, by means of a short and conclusive argument, that a heavier body does not move more rapidly than a lighter one provided both bodies are of the same material and in short such as those mentioned by Aristotle.
First, Aristotle does not say ‘We see the heavier’ at any point; where he does describe his observations of buoyancy, they are strictly accurate. And second, ‘a heavier body ... [and] a lighter one provided both bodies are of the same material’ is exactly not ‘such as those mentioned by Aristotle’. What Aristotle actually says is: ‘two bodies endowed with weight and equal in bulk’ (δυοῖν ἐχόντων βάρος καὶ τὸν ὄγκον ἴσον).

Galileo, who was not a well-mannered man at the best of times, is arguing against what he imagines Aristotle said. Recent figures like Russell, Butterfield, Skinner, and Hawking are following all too closely in Galileo’s footsteps: in misrepresenting an exceptionally clear-headed researcher who was an empiricist, albeit one who made mistakes; someone whose chief flaw was that he sometimes trusted reports of observations which, in hindsight, he should not have trusted.

Put another way: taking other people’s reports on faith is a flaw shared by Aristotle, Skinner, and Hawking. If that makes Aristotle the scientist who got everything wrong, doesn’t it do the same for Stephen Hawking?

Wednesday, 30 August 2017

Roman plagiarism of Greek gods

Left: Poseidon (Melos, late 2nd cent. BCE, National Archaeological Museum of Athens). Right: Neptune (Trevi fountain, Rome, 18th cent. CE).

One of the first things a student of classical Greco-Roman mythology learns is that the Greeks and Romans talked about the same gods, but with different names --

Greek Roman god of ...
Zeus Jupiter sky, lightning, king of gods
Demeter Ceres agriculture, grain crops
Ares Mars war
Poseidon Neptune sea, earthquakes
Aphrodite Venus sex, erotic desire

and so on. A very few gods, like Apollo, keep the same name. Every myth course starts with a table like this.

So if stories about Zeus, Hermes, and Herakles are the same thing as stories about Jupiter, Mercury, and Hercules ... and the Greeks came first ... that means the Romans stole their mythology from the Greeks, right?

Well, if it were right we wouldn’t be here talking about it. Plenty of sources out there on the web point out that some of the Roman pantheon were native Roman gods, like Quirinus, Bellona, and Terminus. But even they’re seen as exceptions to the rule. Those few are the genuine Roman gods -- not like those other mainstream gods ...

Now, it is true that many of the resemblances between the Greek and Roman pantheons are no coincidence. But the Romans didn’t replace their own gods, and they didn’t steal Greek religion either.

... except when they did. I have to add a caveat: there are a few cases where the Romans really did appropriate Greek gods or Greek religious cults. But not as many as you think, and not the gods you’re thinking of. Let’s look at some reasons for the resemblances.

1. Indo-European religion

Names of gods, and in some cases maybe other aspects of them, can sometimes be traced back to prehistoric origins. This works the same way that historical linguists reconstruct family-trees of different languages. In this way of looking at things, you could imagine the Greek and Roman gods sort of as cousins.

To an extent, at least. You have to be careful: prehistoric Indo-European links aren’t as pervasive as people sometimes imagine.

For gods with related names, we only have a couple of really good examples. The best known is Zeus-Jupiter. Both of these names can be traced back to a reconstructed Proto-Indo-European name *dyēus-ph2tēr, where *ph2tēr = ‘father’. The name also shows up in India as the Vedic god Dyauṣ Pitā, and in a few other places too. In Zeus’ case, the ‘father’ dropped off (though he’s still regularly called ‘father of gods and men’) and the *dy- metamorphosed into either dz-, sd-, or di-, depending on the dialect and on his grammatical role in a sentence. In Jupiter’s case, the *d- disappeared, and the -ēu/ēw- got assimilated with the following -p-, resulting in -upp- followed by a neutral vowel: Iuppiter. In other grammatical forms, the -pater disappeared too, resulting in the stem Iov- (originally pronounced yōw-). That’s why even in English he can be called either Jupiter or Jove.

Another pair that’s obviously related is Hestia-Vesta. There’s some evidence to suggest a prehistoric Greek goddess called Eleuthera, and one of Jupiter’s cult titles in Latin is Liber: both mean ‘liberator’ in their own languages. [correction:] we know of Latin vegetation gods called Liber and Libera: all of them come from an Indo-European root meaning ‘growth, increase, the people’. [end of correction] And there’s some sort of connection between Greek Eos, Latin Aurora, Vedic Uṣas, and Lithuanian Aušrinė, but in their case it’s questionable whether they derive from an Indo-European goddess or from an Indo-European word meaning ‘east, dawn’: Eos, Uṣas, and Aušrinė don’t have much in common, and we know basically nothing about Aurora.

But for most gods, the name game doesn’t work. ‘Athena’, ‘Demeter’, ‘Dionysus’, ‘Hera’, ‘Hephaistos’, and ‘Hermes’ all appear to have non-Indo-European roots -- mixed with Indo-European elements, in the cases of Demeter and Dionysus (*meh2tēr ‘mother’, dio- ‘of Zeus’) -- and ‘Apollo’ and ‘Poseidon’ have uncertain origins. On the Roman side, ‘Juno’ and ‘Minerva’ both have known Etruscan precursors, which is to say, not Indo-European; ‘Ceres’, ‘Mars’, ‘Venus’, and ‘Vulcan’ come from Indo-European words, but we don’t find any related names among other Indo-European gods of grain, war, sex, and fire.

There are more options when we look at religious practice, divine functions, and story-elements. For example, Zeus and Jupiter both have cult titles built out of verbs: Zeus can be ‘Zeus the Gatherer’, ‘Progenitor’, or ‘Saviour’; Jupiter can be ‘Victor’, ‘Helper’, and ‘Adviser’. Zeus is a Greek sky god who was nursed by a goat as a baby, and gets called aigiochos, ‘goat-rider’ or ‘goat-driver’; Thor is a Norse sky god who drives a chariot drawn by goats. When Zeus enters a gathering of the gods in Homer, they all stand up for him; the same happens for Indra in the Indian Mahābhārata, and for Ea in one Hittite text.

For Roman mythological elements, it’s harder to find Indo-European parallels. This is partly because there’s a severe shortage of information about gods in early Rome. The Greeks had myth encyclopaedias, and scholarly investigations of their own mythology: we have a huge amount of information from them. But from the Romans, not so much. There are snippets in writers like Servius and Pliny, but nothing as systematic as the Greek mythographers. Partly it just comes down to the sheer amount of text that survives: we have about eight times as much textual sources from the Greek world as from the Latin world. Varro, one of the greatest scholars of Greco-Roman antiquity, wrote a long treatise on early Roman religion called Antiquities of divine matters, which ought to be a key source for Roman religion ... but, alas, it doesn’t survive.

2. Interpretatio romana

Most ancient cultures had different names and even different stories about the same gods. ... So as the Romans conquered the Greeks they adopted Greek Mythology and replaced the gods’ names with traditional Roman gods’ names. Similar process would occur when the Germanic tribes were Romanized.
-- ‘Farhan Elohovitch’, Quora.com, June 2016
Ancient Mediterranean civilisations who were in touch with one another often drew parallels between their pantheons and equated them with each other. When the Greeks looked at Egyptian mythology, they saw some parallels between Egyptian gods and their own gods, so they ended up referring to the Egyptian gods by Greek names: Zeus = Amun, Apollo = Horus, Adonis = Osiris, and so on. Nowadays we call this interpretatio graeca. There was no danger of mixing the gods up, because the resemblances weren’t very deep, and because the different names were linked to different places. Ancient religion was often more about observing local customs than about belief: when in Egypt or Libya, you visit the oracle of Amun; when at Dodona in Greece, you visit the oracle of Zeus.

In the same way, the Romans referred to foreign gods using Roman names. When talking about the Greek Zeus, they’d call him Jupiter; when talking about the Greek Hephaistos, they’d call him Vulcan. And there was an awful lot of Greek myth floating around, so it’s not really surprising to find Romans telling Greek stories with Roman names. Again, this was more a terminological thing than a religious thing.

The Romans did this with other pantheons too. Julius Caesar’s account of Gaulish religion refers to the Gaulish gods by Roman names (Gallic wars 6.17): he says their chief gods were Mercury, Apollo, Mars, Jupiter and Minerva. These could be Lug, Belenus, Teutates, and Sul; but the interpretatio romana of Gaulish gods wasn’t nearly as one-to-one as it was with the Greek pantheon. The equations changed depending on time and place. Teutates could at times be equated with any of Mercury, Mars, and/or Jupiter, and the Gauls had many gods of healing to equate with Apollo.

It is fair to say that in the Roman-Greek case, the resemblances are relatively accentuated by comparison with the Greek-Egyptian or Roman-Celtic cases. Roman religion was unquestionably something very distinct from Greek religion; but elite Roman literature very often took stories about the gods from Greek sources. When Ovid tells stories about gods using Roman names, he’s telling Greek stories; but that has little if anything to do with Roman religion. Elite, high-faluting poetry is not the same thing as religion.

3. Genuine adaptations

We know that the ancient Greeks had a massively entertaining sets of gods and goddesses. So it’s no wonder that when Rome conquered Greece, they replaced their own dull pantheon with renamed versions of Zeus, Athena, and the others. But not all Roman gods were Greek copies ...
-- Rob Bricken, io9, Jan. 2015
Some Roman gods genuinely were borrowed, inherited, or copied from the Greeks. Apollo is the most famous case, but there are some other significant ones. The divine twins, Castor and Pollux, were extremely important very early on, in the battle of Lake Regillus at the very beginning of the Roman republic in 495 BCE; and they were definitely not home-grown. They were borrowed from the Greeks, either directly or via the Etruscans. This goes for some important heroes, too, especially Hercules, Aeneas, and Ulysses: Ulysses had a significant role in Roman legend as early as the sixth century BCE, and evidence for Aeneas pops up quickly afterwards (during the reign of king Tarquinius Superbus the Romans founded a colony named after Circe at the supposed location of Circe’s island; one 5th century Greek source, subscription needed, tells us that Aeneas and Ulysses founded Rome together, and a Hellenistic poem has them meeting up near the future site of Rome). Later on, Dionysus-Bacchus became another major import.

But a couple of cautions are warranted. First, it wasn’t a one-way street. Greeks colonised Italy, but Italians visited Greece too: one inscription from ca. 500-470 BCE shows ‘Tyrrhenians’ (Etruscans? native Campanians?) dedicating an offering to Apollo at Delphi. The Latin demigod Faunus shows up in Greek as ‘Agrios’, alongside Latinus, in a passage that got added to the Hesiodic Theogony probably in the late Archaic period.

In Rick Riordan’s third series of demigod novels (The Lost Hero, 2010) the Roman gods are more variations on a theme than a truly distinct pantheon: Ares and Mars have different personalities, but the same face.
And second, the borrowings weren’t just about the Greeks. The cults of Isis, Cybele, Mithras, and Christ were ‘borrowed’ in exactly the same way as Apollo or Bacchus. Yet somehow you don’t hear people complaining that the Romans ‘stole’ Christianity, or ‘replaced’ their own gods with Christ. With the relationship between Roman and Greek religion, the fashion is to assign agency to the Romans: the Romans stole, or borrowed, or adapted the Greek gods. Yet somehow when it comes to Christianity you’ll often find Christianity as the agent: Christianity expanded, it rose to prominence, it took over the Roman empire. (Did I say ‘somehow’? Well, actually there’s no real uncertainty: blame Gibbon.)

Saying ‘the Romans stole their gods from the Greeks’ makes about as much sense as saying ‘Peter Jackson stole New Zealand cinema from Hollywood.’ It’s nonsensical to talk about theft or appropriation when you’re talking about cultural hegemony. For 6th-century BCE Italians, the Greeks had that hegemony, in much the same way that Hollywood has it in 21st-century New Zealand.

Later, especially in the Pyrrhic War of the early 3rd century BCE, it looks very much as though the Romans took pains to reject Greek cultural hegemony, or at least western Greek. That appears to be when they came close to erasing Odysseus-Ulysses from Roman legend. Aeneas was left as the only ancestral figure: traces of Odysseus-Ulysses remained only outside Rome. His and Circe’s son Telegonus was the legendary founder of Tusculum, and in some sources Caere and Praeneste; in another source, Odysseus himself was buried at Cortona. These cross-overs between Italian geography and Greek mythical figures aren’t an act of Roman cultural appropriation: they’re a collaboration between Greek writers and Italian legends -- just as The Lord of the Rings trilogy is a collaboration between Hollywood and ‘Wellywood’.

Tuesday, 15 August 2017

Volcano Day

‘Pompeii ... we’re in Pompeii! And it’s Volcano Day!’
Doctor Who, ‘The fires of Pompeii’ (2008)
Warning: this blog post is wrong!

After I posted it, the archaeologist Sophie Hay alerted me to an article, Abdy 2013, which entirely tears out the rug from the central piece of evidence discussed here. The coin which I refer to as ‘minted no earlier than September 79 CE’ actually comes from an earlier issue. The inscription, illustrated and reported below as containing the phrase Imp XV ‘(recognised as) general 15 times’, actually reads Imp XIIII ‘general 14 times’, and there is no PP at the end. The poor state of preservation of the coin misled some very skilled numismatologists ... and I am no numismatologist.

Coin struck from the same reverse die as the coin found at Pompeii. In the case of the Pompeii coin it was originally thought that the number after IMP must be XV, because the capricorn’s tail would block any longer number. In this better preserved coin, however, notice that the XIIII actually crosses the tail. According to Abdy 2013, the Pompeii coin actually dates to July or August 79 CE.(Source: Abdy 2013, Plate 18)
I shall leave the post up, unedited, as a monument to my capacity for being completely wrong!

-- PG, ca. nine hours after post first went up


The eruption of Mt Vesuvius in 79 CE, which wiped out the city of Pompeii, is famously recorded in an eyewitness report by Pliny the Younger, Letters 6.16. Pliny tells the story of how his uncle, Pliny the Elder, the famed collector of facts, factoids, and oddities, launched a rescue expedition, in the course of which he died from causes apparently related to poor respiration.

Let’s talk about the date of the eruption. According to mainstream tradition, it happened on the 24th of August, 79 CE. This is the date Wikipedia reports, and the date that appears in every edition of Pliny’s Letters. Wikipedia also adds a caveat, ‘(probable)’, and has a substantial section devoted to doubting the date. Still, it leaves a final impression that the evidence is inconclusive. Readers will probably come away feeling free to go on quoting the date as 24 August -- maybe with a ‘(probable)’ warning at most.

In fact the evidence is entirely conclusive: the 24 August date is very definitely wrong. It’s just that among all the discussion, it may be difficult to see what the really decisive piece of evidence is. That’s also the case in the only academic discussion that the Wikipedia discussion cites, Rolandi et al. 2007. Rolandi et al. present loads of information, but their aim isn’t to weigh up which piece of evidence is the most important. But here’s a hint: it’s not the one in the headline of the article (‘the southeast tephra dispersion’). Judging from the Wikipedia article, it looks like it isn’t easy for a layperson to make out the smoking gun amidst the clouds of volcanic sulphur.

The really decisive piece of evidence is this: a coin, which was found in a hoard belonging to victims of the eruption, and which was minted no earlier than September 79 CE.

That’s the one item of evidence that points unambiguously to a later date for the eruption. Everything else is supporting evidence. Climate conditions and the locations of pyroclastic fall deposits; textual evidence in manuscripts of Pliny’s letter; food items found at Pompeii; styles of dress found on the bodies of the dead ... those things are all well and good, sure. But they’re all secondary to the direct and nearly explicit evidence of that coin. They’re helpful to the extent that they make the coin’s evidence more plausible, not because they’re more important than that coin.

(For similar assessments see Beard 2008: 17-19; Lazer 2009: 79-80. They mention all the other evidence, but like me, they both conclude that the coin is ‘[m]ore clinching’ (Beard); ‘This contentious issue may well have been resolved by the ... silver denarius’ (Lazer). If you want another second opinion that’s easier to get at, you can also try this 2013 blog post by ‘Roma Invicta’.)

The traditional date

The traditional date comes from Pliny. Here’s the relevant bit in his letter:
erat Miseni classemque imperio praesens regebat. nonum Kal. Septembres hora fere septima mater mea indicat ei apparere nubem inusitata ...

(My uncle) was at Misenum, on duty in command of a fleet. On the ninth day before the kalends of September, at roughly the seventh hour, my mother pointed out to him that an unusual cloud was appearing ...
-- Pliny, Letters 6.16.4
‘The ninth day before the kalends of September’ is a standard Roman way of reporting the date. The ‘kalends’ were the first day of the month, so the ninth day before that (counting inclusively) was the 24th of August.

Pointing at the coin isn’t going to be enough: we also need to account for Pliny’s testimony. If he says it was the 24th of August, that’s always going to be more explicit than a coin, right?

Well, this is where the manuscripts come in. Looking at actual surviving manuscripts of Pliny shows that it’s extremely unlikely that nonum Kal. Septembres is what Pliny actually wrote. Most manuscripts of Pliny are pretty incoherent about the date, and only one manuscript gives a nice clear-cut text that actually makes sense, and that’s the one that reads ‘24th of August’. Some other manuscripts read novem, which could be either ‘nine’ (‘nine days before the Kalends of September’), which would be an unusual phrasing, or more probably an abbreviation for November, Novem(bres). It may well be that confusion between Novem(bres) and novem has produced nonum (ninth); the phrase hora septima ‘at the seventh hour’ could be responsible for the introduction of Septem(bres).

Realising that this piece of testimony doesn’t actually have much of a leg to stand on is an important component of this argument. It’s still not the decisive point, though. The manuscript readings just remove evidence for the 24 August date; it’s the coin that proves the eruption didn’t happen on 24 August.

Mount Vesuvius looms over the remains of Pompeii

Weighing up the evidence

Here’s the break-down of reasons for doubting the 24 August date, and the different ways in which each reason matters. I’ll give the evidence in the order that Wikipedia mentions it:
  1. Manuscript readings in Pliny Letters 6.16.4 show that the traditional date is poorly supported. They are not in any sense contrary evidence: they don’t disprove the 24 August date. Their role lies in making the positive evidence for 24 August decidedly weak.
  2. Evidence of heavy clothing found on casts of some eruption victims is mildly supportive of an autumn date. This is very far from compelling, since there are plenty of other explanations (there’s always variation in seasonal weather; the people were fleeing their homes, and may have planned for being without shelter). But it is mildly interesting supporting evidence for doubting the August date. Not remotely in the same league as the next two items, however ...
  3. Archaeological finds of autumnal crops, including fruits, hemp, etc., suggest an autumn date for the eruption. These are historically the reason why the traditional date was first doubted, by Carlo Maria Rosini, who excavated Pompeii in the late 1700s. They were decent evidence, and somewhat compelling, but not quite strong enough to counter the Pliny manuscripts that do read ‘24th of August’. Now that stronger evidence has come along, these finds are demoted to being high-quality supporting evidence.
  4. The coin mentioned above, found in 1974, and with a detailed argument published in 2006 by Grete Stefani, director of the Office of Excavation of Pompeii. This coin is the first unambiguous evidence that Pompeii was not buried before September at the very earliest. It is clear-cut, absolutely decisive, and extraordinarily difficult to refute.
  5. Dispersal of pyroclastic deposits. An article published by Rolandi et al. (2007) relies on seasonal wind patterns to argue against the August date. As with item 2, above, this isn’t decisive (I’m not aware of a place that has no variation in seasonal winds ... but then, I live in Wellington), but it is still interesting supporting evidence.
The Wikipedia article demotes the most compelling piece of evidence to fourth place, and devotes more than half of its discussion to the least compelling ones, items 1 and 5. It’s not surprising people are confused.

On the other side we have the evidence in favour of the 24 August date:
  • Pliny Letters 6.16.4: though the manuscript tradition is inconsistent, we do have the date 24 August supported there. Just not strongly.
  • Cassius Dio 66.21.1 states that the eruption took place ‘in the very time of summer-waning’, or late-summer/early-autumn. This would normally put the event between ca. 6 August (the setting of the constellation Lyra, to Pliny the Elder Natural history 18.59) and 25 September (the autumn equinox). Well, it’s consistent with the 24 August date, at least. On the other hand, Cassius Dio also reports that the eruption was preceded by omens of giants stalking the countryside and flying overhead (66.22.2) ...
Yeah, these points are pretty weak. They certainly don’t stand up to the overwhelming evidence of the coin, and the supporting evidence from archaeological finds of seasonal crops.

The coin

Two coins of emperor Titus, one (top) showing Titus recognised as imperator (‘general’) fourteen times, the other (bottom, outlines enhanced) the coin discussed by Stefani 2006, showing Titus recognised as imperator fifteen times, and therefore dating no earlier than September 79 CE.
Top: Heads side reads Imp Titus Caes Vespasian Aug PM, ‘Gen(eral) Titus Caes(ar) Vespasian(us) Aug(ustus), p(ontifex) m(aximus).’ Tails reads TrP VIIII Imp XIIII Cos VII PP, ‘Tr(ibunician) P(ower) 9th time, (hailed as) gen(eral) 14th time, cons(ul) 7th time, f(ather of his) c(ountry).’
Bottom: Heads side same as above. Tails reads TrP VIIII Imp XV Cos VII PP, ‘Tr(ibunician) P(ower) 9th time, (hailed as) gen(eral) 15th time, cons(ul) 7th time, f(ather of his) c(ountry).’
The bottom coin is the important one. It was found in 1974 next to the so-called House of the Golden Bracelet, along with about 200 other coins that victims of the eruption took with them as they fled. No, it’s not the most beautiful coin ever designed. Titus has quite the neck there, doesn’t he? But it’s neatly unambiguous: as the inscription on the tails side says, when it was minted (or, arguably, just about to be minted), Titus had been recognised as imperator (‘general’) fifteen times.

How does it have a bearing on the date? It’s because we know that as late as 8 September 79 CE, official Roman documents were still referring to Titus as imperator for the fourteenth time. In particular, the emperor’s own office was still calling him imperator for the fourteenth time on 7 September.

This is not something that can be chalked up to news travelling slowly: changes in who was emperor and the emperor’s status were circulated around the empire very promptly. For example, we have papyri from Egypt reporting on new emperors within a month or so of their taking the position. And Pompeii is a lot closer to Rome than Egypt is. And with a coin, you also have to add in extra time for it to be minted and get into circulation and into someone’s purse.

The documents in question are two inscriptions. One is a military diploma found in Egypt dating to 8 September (line 17: a(nte) d(iem) VI Idus Sept(embres)); that could be blamed on communication delays between Rome and Egypt. The other is much more compelling: it is a letter on a bronze tablet sent from the office of the emperor himself and dating to 7 September (line 16: dat(um) VII Idus Septembr(es)). So unless we’re going to argue that the emperor’s own secretarial staff had somehow forgotten there had been a fifteenth acclamation as imperator, we have absolutely rock-solid evidence that Pompeii was still unburied when the letter was sent on 7 September.


Endnote

As noted at the beginning of this post, this post is wrong! The coin highlighted as the central piece of evidence here was misidentified, and the misidentification was only realised in 2013. See Abdy 2013, and some further details at the beginning of this post.

References

  • Abdy, R. 2013. ‘The last coin in Pompeii: a re-evaluation of the coin hoard from the house of the Golden Bracelet.’ Numismatic Chronicle 173: 79-83.
  • Beard, M. 2008. Pompeii. The life of a Roman town. London: Profile Books.
  • Borgongino, M.; Stefani, G. 1999. ‘Intorno alla data dell’eruzione del 79 d.C.’ Rivista di studi Pompeiani 10: 177-215.
  • Lazer, E. 2009. Resurrecting Pompeii. London/New York: Routledge.
  • Rolandi, G.; Paone, A.; Di Lascio, M.; Stefani, G. 2007. ‘The 79 AD eruption of Somma: the relationship between the date of the eruption and the southeast tephra dispersion.’ Journal of Volcanology and Geothermal Research 169: 87-98.
  • Stefani, G. 2006. ‘La vera data dell’eruzione.’ Archeo 206: 10-13.
  • Stefani, G.; Borgongino, M. 2007. ‘Ancora sulla data dell’eruzione.’ Rivista di studi Pompeiani 18: 204‑6.

Wednesday, 14 June 2017

Greek contempt for archers

Vain archer! trusting to the distant dart,
Unskill'd in arms to act a manly part!
Thou hast but done what boys or women can;
Such hands may wound, but not incense a man.
Nor boast the scratch thy feeble arrow gave,
A coward's weapon never hurts the brave.
-- Alexander Pope, The Iliad 11.493-8
(inspired by Homeric Iliad 11.385 and 388-90)
In the Iliad, these words are spoken in battle by the hero Diomedes, straight after he has been injured by an arrow. It's not surprising he's cross. The question is whether his animus against archers is typical. Did the Greeks despise archers?

Heracles shooting arrows: sculpture from east pediment, temple of Athena Aphaia, Aigina, ca. 500-480 BCE. Glyptothek, Munich (source: Wikimedia.org)

Spoiler alert: it's pretty much a myth. It's not quite simply flat-out false: it's at least true that different weaponry kits did have certain social implications. But it definitely wasn't a case of 'swords good, bows bad'. The position of archery in ancient Greek perceptions of warfare isn't a matter of moral character, and it doesn't have its roots in aristocratic prestige. It's about economic practicalities and material costs.

Yes, ancient sources will occasionally set archers in opposition to hoplites -- that is, spear-warriors, like the Spartans in the film 300 -- but if you read those sources in context, they're never quite that straightforward. In the Iliad passage, above, Diomedes' critique of archery comes in the context that an archer has just successfully beaten him in combat. Of course he's cross at archers!

Some relatively experienced people fall for the myth too. Here's one writer who should know better:
When the hoplite dominated Greek warfare, archers were generally looked down upon as men who lacked the bravery to engage in hand-to-hand combat. A fairly typical utterance is 'the measure of a man is not archery; rather he who stands fast in his rank and gazes unflinchingly at the swift gash of the spear [is a brave man]' (Euripides, Heracles, 190-192). This attitude may have existed as early as the Lelantine War if the evidence for the ban on missile weapons during this conflict has any value. The attitude probably developed even further with Greek exposure to foreigners such as the Persians and Scythians, who used the bow and not the spear as their principal weapon.
-- Iain Spence, Historical dictionary of ancient Greek warfare (2002), p. 59
Spence treats the status of archery as purely a moral thing, and that distorts things badly. First, an incidental correction: Spence's Euripides quotation comes from Heracles lines 162-4, not lines 190-2.

1. Says who? Spence treats the sentiment as 'typical'. This requires forgetting that the speaker in the play, Lycus, is no ethical paradigm: he's unquestionably a villain, a usurper and tyrant, who wants to murder Heracles' family unjustly, for no reason other than just to be a complete bastard. He is not typical.

2. Fair and balanced? Haha, no. Picking out Lycus' testimony is a really really bad case of cherry-picking. Spence cites Lycus' words at 162-4, but neglects to mention lines 188-203, where Amphitryon answers Lycus' claim and rejects it completely. Amphitryon speaks of a hoplite as someone who is 'slave to his arms' and to his neighbours in the battle-line. He also argues that archery is tactically superior. That doesn't mean that's Euripides' own verdict on the subject, of course! But it does show that it's tendentious to call Lycus' words 'a fairly typical utterance'. Amphitryon, the good guy of the scene, gets the last word.

3. The Lelantine War. Spence's second piece of evidence is a treaty according to which archery was supposedly banned during the Lelantine War. Even at the best of times, the Lelantine War poses historiographical problems. It's a very early war, and our earliest testimony about it is nearly 200 years later than the war itself. Evidence for the supposed archery ban is weaker still -- so weak that it undermines the story more than it supports it. The earliest sources for the war, Herodotus and Thucydides, make no mention of any ban. The ban only appears in Polybius and Strabo, another few centuries later. And Strabo's testimony makes it clear that the alleged treaty wasn't about archery, but about all forms of ballistic missile -- and at the time of the war, that would have included spears as well as bows! In other words, this supposed treaty banned both of the two weapons most commonly associated with aristocratic warriors. In the present day, consensus is that the ban was almost certainly invented by Polybius' and Strabo's source, Ephorus of Cyme, a historian who wrote ca. 350 BCE, some decades after Herodotus and Thucydides. Why did Ephorus come up with the story? Well, in light of Strabo's reference to all missiles rather than bows and arrows, Wheeler (1987) suggests that Ephorus' concerns were probably not about archery at all: he may have been thinking of early 4th century BCE developments in large artillery.

Odysseus slaughters the suitors: illustration by John Flaxman, 1805 (photo © Tate, CC-BY-NC-ND 3.0 (Unported))

In 5th century BCE sources it is possible to detect a less high regard for light-armed troops than for hand-to-hand hoplites. That's not really about archery, though: it's more to do with the class connotations of being a hoplite. Hoplite arms were very expensive -- much more expensive than being a slinger, or what the Greeks called a peltast (peltastēs), that is, a javelineer. Hoplites were more prestigious because they were richer; light-armed troops were proles. It wasn't about archery itself, it was about economic class. That didn't stop 5th-4th century combatants from recognising the advantages of ranged warfare (see for example Xenophon Anabasis 3.3.6-10). In the late 5th century, throughout the Peloponnesian War, whenever hoplites came into conflict with light troops, the hoplites consistently got massacred if they didn't have support from their own light troops or cavalry. The first ever time that a band of Spartan hoplites threw down their shields and surrendered unconditionally in a land battle was when they were utterly trounced by an army consisting of archers, peltasts, and slingers. It's hard to argue with success.

I wonder if people are tempted to see hoplites of the Classical period as successors to Homeric heroes. Well, in a way: there's a certain continuity in their armour. But not in their tactics. Hoplites fought in phalanxes; Homeric heroes fight in melee (or if they do fight in phalanxes, it's far from obvious). And they don't use their spears in hand-to-hand combat, as Classical hoplites did. They throw them. Homeric heroes are all warriors-at-a-distance.

Now, that's not to say that Achilles is a peltast. Iliadic combat is in a kind of in-between state. At the time of the Iliad, in the second quarter of the 7th century BCE, Greek warfare saw a transformation in the use of spears: pictorial depictions show a transition from soldiers holding multiple spears, evidently for throwing, to a single spear, evidently for hand-to-hand combat. There are hints of the same transition within the Iliad: in combat, spears are always thrown, but when Patroclus is arming for battle he takes two regular spears rather than Achilles' one special ultra-heavy spear (Iliad 16.139-144; the special spear appears again at 19.387-391); and it's only through divine intervention that Achilles gets to have two spear casts at Hector (22.273-277). Patroclus' two spears sound like peltast javelins; Achilles' one special spear sounds a bit more like a hoplite weapon.

Be that as it may. Spear-throwing is relevant -- it would have been banned under the mythical Lelantine War treaty, remember -- but it's archery that we're here to talk about.

Archery was prestigious, not contemptible. Do we really need to spell out that the supremacy of Heracles and Odysseus in battle was largely thanks to their prowess in archery? Or that archery is key to winning the Trojan War in Sophocles' play Philoctetes? Or that one of the most revered gods of the Greeks, Apollo, was an archer god? Or that among aristeiai in the Iliad -- that is, setpiece scenes where a Greek hero excels in battle and goes on a rampage -- one of the outstanding heroes is an archer, Teukros? (a.k.a. Teucer; the brief aristeia is at Iliad 15.442-483, with an arming scene unusually at the end, 478-483.) Or that the greatest warrior at Troy, Achilles, is laid low by an archer? Or that in Archaic depictions of sympotic scenes, when aristocratic homes have weaponry hanging on a wall as decoration, that weaponry will typically be shields, swords, and bows, and only rarely spears?

'Teucer', by Hamo Thornycroft, 1881 (photo © Tate, CC-BY-NC-ND 3.0 (Unported)). (Backdrops can be deceiving: this statue is 2.4 m high!)

No matter how many positive icons I mention, it'll just never be enough, it seems, to dispel the idea that the Greeks despised archers. Because one particular archer outweighs them all in the popular imagination: Paris. Other characters in the Iliad really have it in for him. Diomedes' rant, at the start of this post, is aimed at Paris. And here's how Paris' brother Hector addresses him at one point:
Hector berated him when he saw, using harsh words:
'Wretched Paris! Beauty specialist, woman-crazy seducer,
if only you had never been born, that you had died without marrying!
I genuinely mean that: it would really have been much better
than to be a disgrace and have others roll their eyes at you. ...'
-- Iliad 3.38-42
And so on. Later, Paris' wife Helen scolds him for not being on the battlefield (3.427-436); further on Hector and Helen both lambast him at the same time (6.325-353); and then of course we get Diomedes' rant in book 11.

Other characters' loathing of him is so marked that he seems to have become iconic of all archers. Even within the Iliad, other archers like Teukros and Meriones should show that Paris is no model. And neither Hector nor Helen reproaches him for being an archer. It's only Diomedes that does that, and of course that's because he's just been beaten. In fact, Hector is very complimentary about Paris' abilities in combat (even if Paris wasn't good enough to stand up to Menelaus in a spear-duel in book 3):
In answer shining-helmed Hector addressed him:
'You oddball! No man who is reasonable
would ever dishonour your action in battle: you're a sturdy guy!
It's that you give up willingly, or you're unwilling. That's why my heart
grieves in my spirit, when I hear shameful things about you
from the Trojans, who have long suffering on your account. ...'
-- Iliad 6.520-525
Archery is one of his virtues, not a flaw. It's how he beats Diomedes; one day (not in the Iliad), Achilles himself will become another victim. Paris is so unconquerable with his favoured weapon that one day (again, not in the Iliad), the Greeks will have to bring in another archer specially, just to get rid of him: Philoctetes, armed with the bow and arrows of Heracles himself.

Actually the most damning thing said about archers in the Iliad has nothing to do with Paris. It's about the Locrians, mainland Greeks led by Aias son of Oileus:
Now, the Locrians were not there with great-hearted Oileus' son:
for their heart did not stand fast in close battle,
for they didn't have bronze horse-haired helmets,
and they didn't have circular shields and ash spears;
but in the bow and fine-spun sheep wool (i.e. slings)
they trusted when they came to Ilios. ...
-- Iliad 13.712-717
Not sturdy enough to be there with the front fighters -- sounds pretty bad, doesn't it? (Note, incidentally, how being in the front line involves using a spear? That ain't how people use spears in the Iliad...) Yet even here, the narrator recognises that it's more about tactics than about prestige. Of course you don't put slingers in the front line. Once again, it's hard to argue with success --
... As a result, with those (weapons)
they would break through the lines of the Trojans by shooting.
-- Iliad 13.717-718

References

  • Van Wees, H. 1994. 'The Homeric way of war: the Iliad and the hoplite phalanx.' Greece & Rome 41.1: 1-18, 41.2: 131-155.
  • Wheeler, Everett L. 1987. 'Ephorus and the prohibition of missiles.' Transactions of the American Philological Association 117: 157-182.

Tuesday, 30 May 2017

Did Thales predict a solar eclipse?

In the late afternoon of 28 May 585 BCE, a total solar eclipse took place over central Anatolia. It is widely believed, almost certainly rightly, that a reference to this eclipse appears in Herodotus:
A war went on between the Lydians and the Medes for five years. The Medes often beat the Lydians, the Lydians often beat the Medes. There was even a night battle, of a sort. They were evenly matched in the war, and when there was an encounter in the sixth year, during the battle it happened that day suddenly became night.
-- Herodotus 1.74
Herodotus, writing about 160 years after the event, goes on to tell us that the Lydians and Medes were so impressed by this that they got two external arbitrators to broker a peace treaty between them, with marriage ties.

What are we talking about, exactly?

Even at this point, there's room for endless quibbling:
  • Where did the battle take place? It's often thought to have been at the Halys river (the modern Kızılırmak), but that's just a guess based on the fact that the Halys was an important natural boundary to Lydian territory.
  • Which eclipse was it? Several other candidates have been proposed. For the record, the 585 BCE eclipse is by far the best choice. Here are maps from Gautschy 2012 showing the path of the moon's shadow for each of the eclipses that have been proposed: 30 Sep. 610; 18 May 603; 28 May 585; 21 Sep. 582; 16 Mar. 581. Note that e.g. '-584' = 585 BCE. The path of the moon's umbra (path of totality) is shown in red; surrounding lines indicate magnitude 0.9, or 90% totality; 0.8; 0.7; and 0.5. Around 600 BCE there's about 2° uncertainty in longitude -- ΔT, as the astronomers call it -- and this is reflected in the multiple bands of red, for the possible paths of totality. The trouble is that while the competing eclipses would have been visible, not one of them would have produced significant dimming. Hughes (2000) has calculated that, based on human perception of ambient lighting, anything less than a 3 point change in the sun's apparent magnitude may go completely unnoticed unless you happen to look directly at the sun and directly observe that it is partly hidden. And, Hughes goes on to show, this corresponds to an eclipse of magnitude 0.937 or greater -- that is, concealing 93.7% of the sun. (Remember that stellar magnitude is a logarithmic scale.) None of the other four eclipses achieved better than magnitude 0.7 -- a change in the sun's brightness of only 1 point of magnitude. The dramatic dimming associated with total eclipses is very sudden, and only happens within about four minutes of totality.
Graph from Hughes 2000, showing eclipse magnitude (= α/2) versus brightness (sun's apparent magnitude). Coloured elements are added by me, with approximate figures for eclipse magnitudes as seen in north-central Turkey based on Gautschy 2012.
  • Was it actually a solar eclipse? Herodotus says 'the day suddenly became night' (τὴν ἡμέρην ἐξαπίνης νύκτα γενέσθαι). He uses the same phrasing about the same battle at 1.103, and when talking about a different incident in 480 BCE at 7.37. The trouble is, there was definitely no historical eclipse corresponding to the incident in 7.37. Herodotus uses slightly different phrasing at 9.10 ('the sun became dim in the sky', ὁ ἥλιος ἀμαυρώθη ἐν τῷ οὐρανῷ), and that could conceivably be a mag. 0.6 eclipse on 2 October 480 BCE -- except that a 0.6 eclipse wouldn't produce significant dimming. And none of these are remotely as clear as Thucydides' descriptions of partial solar eclipses on 3 August 431 (Thuc. 2.28; mag. 0.88) and 21 March 424 (Thuc. 4.52; mag. 0.71), or a lunar eclipse in the wee hours of 28 August 413 (Thuc. 7.50; total).
But let's leave all that for now, because it's just good old debate and no one's in any danger of serious misunderstandings from it. The thing that makes Herodotus' eclipse famous -- we'll take it for granted for now that it was an eclipse -- is that he also tells us that it had been predicted beforehand by Thales, a Greek sage.

Herodotus' report

Herodotus isn't the only source to tell us that Thales predicted an eclipse. But all the other relevant sources are very probably derived entirely from Herodotus, with some distortions along the way. So they're not independent: they have very little corroborative value, if any. Still, here they are, for what they're worth, in chronological order:
Clement, in particular, indicates that an important lost source, Eudemus of Rhodes (4th cent. BCE), was simply based on Herodotus. The only hint of independence here is in Cicero, who states that Astyages was on the Lydian throne at the time of the incident: in Herodotus, Astyages' father Cyaxares was still around. In other respects, unfortunately, Cicero's report is terse and vague.

The upshot is that we depend entirely on Herodotus for an account of what Thales actually predicted. So let's take a look at what Herodotus actually says:
τὴν δὲ μεταλλαγὴν ταύτην τῇ ἡμέρης Θαλῆς ὁ Μιλήσιος τοῖσι Ἴωσι προηγόρευσε ἔσεσθαι, οὖρον προθέμενος ἐνιαυτὸν τοῦτον ἐν τῷ δὴ καὶ ἐγένετο ἡ μεταβολή.

Thales of Miletus had advised the Ionians in advance that this transformation would happen, setting this year as a boundary, in which the change did in fact take place.
-- Herodotus 1.74
'Setting this year as a boundary'? This is not a report of someone predicting that an eclipse -- or whatever it was -- would happen on a specific day. What Herodotus actually claims is that Thales predicted in which year this 'transformation' would occur. To call that 'predicting an eclipse' is a colossal stretch.

How could Thales have predicted an eclipse anyway?

The simplest customary answer to this question is: he must have discovered that solar eclipses come in Saros cycles, just like lunar eclipses do.

A Saros cycle is a period of 223 lunar months which governs all eclipses, both solar and lunar. This period is determined by three simultaneous periodic movements of the earth-moon-sun system (the moon's orbit relative to the sun, the moon's orbit relative to the stars, and orbital precession) which which come very close to coinciding with one another after 223 lunar months.

In other words: if you have an eclipse at t = 0, you will have another eclipse at t = 18 years, 11 days, 7 hours, and 42 minutes. (Subtract one day if that period includes five leap years.) A Saros series doesn't last forever, because those periodic movements I mentioned aren't perfectly regular -- but it's pretty close: it will last for 1230 to 1550 years. Plenty long enough for ancient astronomers to notice it!

And, indeed, long before Thales came along, the Babylonians had already discovered the Saros cycle as it relates to lunar eclipses. So, hey, it's obvious: Thales must have discovered that solar eclipses follow the same cycle, right?

And that would be absolutely completely dead wrong. Here's why. A lunar eclipse is when the earth casts its shadow on the moon. As a result, the eclipse is visible from anywhere on that side of the earth. A solar eclipse is when the moon casts its shadow on the earth. As a result, the eclipse is only visible on that part of the earth which happens to be shadowed by the moon.

The solar eclipse of 8-9 March 2016, as viewed by the NASA-NOAA Deep Space Climate Observatory (DSCOVR). (source: Space.com)

If you see a solar eclipse at the start of month 0, it's possible to see another eclipse 223 months later. But, because the Saros cycle isn't perfectly regular, you'll only see the second eclipse if you move south and west far enough to compensate for that irregularity, and for the fact that the end of the lunar month will fall 7 hours and 42 minutes later in the day. Solar eclipses may happen every 223 months, but there's absolutely no possible way for an ancient astronomer to have seen them every 223 months.

But wait, not so fast. If the 223 month period means that each eclipse is 7 hours and 42 minutes later in the day, that'll eventually wrap round, right? After three Saros cycles, you'll get another eclipse that's 23 hours and 7 minutes later -- pretty close to 24 hours. Put another way, you'll get an eclipse that's 53 minutes earlier in the day. That could be a realistic way to see solar eclipses! And in fact Greek astronomers had a technical term for this period of three Saros cycles, 669 lunar months or 54 years and 32 days: they called this period an exeligmos.

But wait again: yes, the exeligmos cycle was known to Greek astronomers -- 500 years after Thales' time, mind -- but to predict an eclipse on 28 May 585 BCE using the exeligmos cycle, you would need to have observed the eclipse one exeligmos earlier on 26 April 639 BCE. Unfortunately, that eclipse never got as far as Thales. Sunset intervened. The eclipsed sun set below the horizon while the moon's shadow was still over Estonia. Eclipses before that are even worse: the earlier in the exeligmos series you go, the earlier sunset puts an end to the eclipse.

This is why many people who have faith in Thales -- or rather, Herodotus' vague and poorly described version of Thales -- tend to opt for other eclipses. The 28 May 585 BCE eclipse is actually pretty hard to predict. But as we saw earlier, none of the rival candidates would have darkened the sky noticeably.

No one has any good theories on how Thales might have predicted the 28 May 585 eclipse. The astronomer Miguel Querejeta (2011) has rejected two leading candidates, and one of the targets of his criticism, Couprie (2004), rejects several more.

One thing is certain: there were no genuine techniques in Thales' time for predicting solar eclipses. Genuine predictions didn't start to emerge until around the 4th century BCE in Babylonian astronomy, and the 3rd century CE in Chinese astronomy (Steele 1997, 1998). The simple reason is that solar eclipses are really sodding hard to predict: because they are very localised, they require an awful lot of very precise observations, and observations of them are very tightly constrained by the geographical location of the observer.

We'd better not go too hard on Thales, though. He may not have predicted an eclipse -- and there's not much reason even to think he did, given how vaguely Herodotus describes his 'prediction' -- but he was a creature of his time. Like all Greek thinkers until the late 400s BCE, he imagined the earth as a flat disc: he believed the earth was like a wooden disc floating in water, as Aristotle and other later writers report (Couprie 2011: 63-7; see Thales frs. A.14, A.15 Diels-Kranz). On the other hand, we have testimony suggesting that he did get some things right. We have (1) two reports that Thales explained the light of the moon as the moon being illuminated by the sun (fr. A.17b D-K; p. Oxy. 3710, col. ii lines 38-43); (2) one report that he explained solar eclipses as being caused by the moon screening the sun (fr. A.17a D-K); and (3) one report that he discovered the periodic nature of eclipses and how 'they are not always exactly equal' (fr. A.17 D-K). What does the last of these mean? Maybe the fact that the Saros cycle isn't an integer number of days. He was no eclipse-predictor, but if half of these reports are true, he was not half bad as an astronomer.

References