G'day Kenny.
The thing that needs to be borne in mind with respect to Spartacus is the relative supermarket his forces had available to him. Holland (
Rubicon - a ripping read) too gives numbers approaching 120,000. What he also gives is a cogent description of Spartacus' "campaign". This began as a rebellion in central Italy with the aim of escaping harsh and brutal treatment. Far from there being any aim to establish the "freedom of the slaves" as such, the refusal to exit Italy via the north – as provided by the defeated home army (the main legions serving overseas) – served to indicate what it had become: a quest to take Rome and essentially place the slaves in the postion of master over Roman slaves. To use Green's words(
Alexander to Actium):
Such men (slaves that were formerly free men, Spartacus et, al) while by no means challenging slavery as an institution, objected violently to being enslaved themselves…Paradoxically, far from wanting to change the class structure of their society, they merely aimed to correct what they saw as an improper skewing of the natural balance between naturally free men and natural slaves.
What then occurs is close to a shortened re-run of Hanibal. Spartacus defeats ill-trained Roman conscript armies and wanders central Italy
looting as he goes. In this case, we can adjudge looting to most definitely include the lightening of Latin larders: crops cattle and fruits. In the end, overconfident, greedy and hubristic Crassus (whose Rumsfeld moment would, coincidentally, come in Mesopotamia) correctly bottled him up in the toe of Italy. Bereft of his larder, Spartacus had to eventually fight and go down as the rabble they had become.
Darius, unlike any of his forbears, had half an empire from which to draw his army and, more importantly, supplies. That half excluded Egypt, Asia Minor and Coele-Syria – a not insignificant part of the Persian larder. Persian armies generally took time to assemble – especially if they included a fleet. For instance, the fleet and army of 397/6 which Artaxerxes II was readying to retake Egypt (the first responsibility, it seems, of every new Persian monarch) was finally commissioned in time to swat Agesilaos' panhellenist adventure by wiping out Spartan naval power in 395/4.
The reason was not, as Herodotus would have it, that such armies were a congeries of human conglomerate rock but rather the distances and armouring involved. At the very basic level, the army needs a supply train of wagons. Such wagons need roads. In the eastern and central parts of the empire, the supply lines for Darius will have been as much a problem for him as for Alexander. The movement of such an army is difficult to imagine: 500,000 at three or four abreast in column would stretch for how many miles? A marching column of four abreast, and separated by one and a half metres would give us a column some 188 kilometres long. Then add the wagons.
It is, though, both the reasonable attested period of the Diadochoi (and other Hellenistic monarchs), the campaign of Cyrus (the pretender, 401) and the Battle of Magnesia (190/189) that give rather furious pause for thought when it comes to the somewhat incontinent figures of Macedonian and Greek sources.
Firstly, at Cunnaxa Cyrus, with his 10,000 and some Greeks holding the right of the field, correctly pins his hopes on these hoplites carrying the day. Noting – as the gap closed between the armies – that Artaxerxes and the Persians (in the middle of the Royal line) would be missed by the Greeks, he orders them to march obliquely towards
the centre. It follows that the Greeks formed the bulk of the right of centre outside of Cyrus' centre. One imagines the army facing it then to be not much, if any, larger. No Greek commander would so precipitously expose a phalanx otherwise.
Secondly, Antigonus, "master of Asia" raises the largest attested army of invasion in 306. For this we have numbers of 80,000 infantry. The figures we have for Ipsus (301) put some 155,000 in action. Raphia (207) saw some 140,000. Ipsus essentially saw all of Asia (aside from "India") engaged. Even were we to add another 50,000 we fall well short of the astronomical 500,000.
Lastly we have possibly the last great Hellenistic monarch, Antiochus III "The Great". In a life or death defence of his empire – larger than was left to Darius in 331 – against Eumenes of Pergamon and Rome, he mustered some 70,000.
I don’t believe that Darius mustered anything like 500,000 at Gaugamela. That, though, is just my view of the evidence.