We have no way of ascertaining the size of Xerxes’ invasion army of Greece in 480–479 bc, which numbered in the millions...
We have no way of ascertaining the size of Xerxes’ invasion army of Greece in 480–479 bc, which numbered in the millions according to Herodotus (7.60–99), or the size of the armies assembled by Darius III against Alexander at Issus (333 bc) and Gaugamela (331 bc), again estimated at 300,000–600,000 and 200,000–1,000,000, respectively, by the Greek sources. Buckets of scholarly ink have been spilt in the effort to make sense of these untenable numbers. Demographic and logistic considerations and comparative deductions would suggest, in my view, that Xerxes’ army may have numbered anything between 100,000 and 200,000 men. For reasons already explained, this imperial army was not overwhelmingly superior in numbers to the combined forces of the Greek militiamen fighting on their native soil, if only the Greek poleis had not been fraught with division among themselves in an all too familiar fashion, many of them allying with the invaders. Darius III’s armies were probably of more or less the same size as Xerxes’, including a few tens of thousand cavalry. All in all, it is not commonly recognized that there were probably more Greeks in the world than ethnic Persians. Indeed, in the huge multi-ethnic levied imperial armies, the relatively small Persian and Mede standing forces, together with the levied Iranian contingents, both horse and foot, were relied upon to shoulder most of the fighting. To these more trustworthy elements were added allied Greeks in Xerxes’ army and Greek mercenaries in later Persian armies, including those of Darius III, troops who increasingly constituted the heavy infantry of the imperial armies.
That’s from the excellent War in Human Civilization by Azar Gat. I haven’t been quoting it here, because most of the interest comes from the way he slowly lays out major cross-cultural similarities in warfare, but it’s a fascinating book and I quite recommend it. It’s perhaps the most Darwinianly fatalistic book about human society I’ve ever read. If you’re interested in, for instance, the way city-states across space and time form, rise, and inevitably fall, this is the book for you.
It feels like this is neglects the fact that the majority of the population in the Achamenid Empire was neither Persian/other Iranian nor Greek, including huge numbers of Semitic people in Egypt and the Fertile crescent, Indo-Aryans in the Indus Valley, and whatever ethnic group(s) were still living in inland Anatolia beyond the Greek colonies (I’m honestly not sure who was there or when they disappeared, but there was definitely someone, maybe descendants of the Hittites) and other relatively minor ethnic groups. This doesn’t seem so bad by itself, but the focus on Greeks seems to me that it might be symptomatic of broader worldview problems like taking a Greco-centric view of the period.
I haven’t read the book so have no idea if this is true or how bad it is, just felt like bringing it up so you can consider that when reading.
This isn’t entirely clear from the quote I posted, but one of the points the author was making is that multiethnic empires weren’t always able to bring as much force to bear as you might expect, since conscripts from conquered peoples made unreliable and ineffective soldiers, and empires often had to rely on fighters from the ruling ethnic group(s) or on foreign mercenaries. That’s why he emphasized how few ethnic Persians there were at the time.
Ah, nice! Glad I asked this. I’m actually not surprised that huge empires weren’t able to bring as much force to bear as most people might expect, but I was assuming it was more to do with the logistics of transporting huge armies relatively large distances and the fact that you simultaneously have to guard against revolts and guard all your other borders while doing so, and the fact that viceroys or nobles in outlying provinces are harder to keep tabs on (to make sure they’re contributing enough soldiers and money); I wouldn’t have thought cultural disloyalty was such a big factor.
Does he have good statistics on what portion of their armies were Persian? Or comparable statistics on something like the Roman armies or the armies of the Diadochi where we have more writing from their perspective?
It wasn’t just disloyalty, he makes it sound like a lack of spirit as much as anything. But he does also list some of those other reasons why empires were less effective at war per capita, including logistics, as well as the fact that citizens of an empire become less adept at fighting as they get used to peace over the generations. For example, by midway through the imperial period, Rome didn’t have a problem with cultural disloyalty, since most of the subject populations had been sufficiently Latinized, but they did have progressive problems getting Romans to fight. First, Italians stopped joining the legions almost entirely. Then the provincials became less warlike over time and barbarian mercenaries had to be brought in. So it wasn’t just the one cause.
He does give numbers here and there, but it’s not primarily focused on that. This is the most he has to say about the makeup of the Persian army:
Most empires possessed a three tier army. [But not Rome, which was fully professionalized.] The first tier consisted of a relatively small nucleus of fully professional troops, mainly comprising a central army/imperial guard. As already mentioned, in the Achaemenid Persian Empire this central standing force appears to have numbered some 20,000 troops, half of them horse and half foot. According to Herodotus, they were called the ‘Immortals’, but his source probably confused the Persian word with a similar one meaning (the king’s) ‘Companions’, which would make much more sense. In Han China, a central standing professional army of roughly the same size as the Persian one was stationed around the capital, augmenting the masses of conscripts.
The second tier consisted of garrison troops in the provinces and on the frontier, to which empires widely applied the principle of military colonists. Although most of the land allotment in return for semi-professional military service was carried out in the frontier provinces, it was also variably practised in the Empire’s heartlands, because the beneficiaries of this system proved somewhat more committed to actually fighting than ordinary imperial levied troops. The system is earliest attested to in Akkad and then in Hammurabi’s Babylonia in the eighteenth century bc, as well as in the Hittite Empire. It persisted in Mesopotamia in Assyrian and Chaldaean times, was taken up by the Persian Empire, and later served the Hellenistic kingdoms for sustaining their mostly Greek and Macedonian colonist–soldiers. The same principle was widely used in China, becoming more prominent during the later Han in inverse relation to the decline of the conscript–militia forces. After a return to militia armies during the Sui and T’ang Dynasties (ad 581–907), the institution of military colonists and military families was revived by the later T’ang, together creating a mixed force pool of about 600,000. A more or less similar force structure was maintained by all subsequent Chinese dynasties, for the same reasons that had handicapped the militia in earlier times. In Indian states, too, military fief holders, maybe those referred to in Kautilya’s Arthasastra (9.2) as ‘hereditary troops’, augmented the royal retinue as a more trustworthy element than the assortment of hired and levied troops.
Third, for large-scale campaigns and during emergencies, levied forces would be assembled and constituted the mass of the army. Native national conscripts from the Empire’s core ethnicity tended to be of at least some military value, depending on the social and geo-strategic circumstances, but they nevertheless played a secondary role to the Empire’s professional and semi-professional forces. Levied short-term conscripts from subject peoples in multi-ethnic empires normally proved to be of very little value. Pressed into battle, they could not be relied upon to do any serious fighting. Although examples abound from across time and space in Eurasia, the multi-national mass armies of the Achaemenid Persian Empire, ‘driven into battle with lashes’, went down in historical memory as typifying such hosts. Their image has survived because the armies were recorded by Greek historians and because both the Persian Empire and its armies were indeed large, although the size of the armies was wildly exaggerated in the Greek sources. Authors invariably exaggerated the enemy’s numbers in pre-modern times, because they both lacked precise information and were patriotically biased.
