Arrian, Anabasis, 1.6.5:
As Alexander saw only a few of the enemy still occupying a ridge, along which lay his route, he ordered his bodyguards and personal companions to take their shields, mount their horses,
Now what needs to be determined is the difference between “personal companions” and “bodyguards”. I’m not able to access the Latinised Greek but I imagine the latter are
somotophylakes and the former
hetairos. I know of no convincing evidence that the companion cavalry carried
apsides into battle (aside from the solitary – and disputed line – in Diodorus’ description on Granicus). My view is that the bodyguards so described are royal hypaspists (the king’s “usual retinue” in Curtius).
Taphoi wrote: Whereas it is not impossible that Alexander had given horses to some of his infantry, it does stretch the meaning of the term infantry in what was evidently a battle situation.
These would be the same “infantry” that Alexander has mount horses “in their normal armour” (or some such) to pursue Darius elsewhere. These, self evidently, are not phalangite “grunts” but hypaspists and almost certainly “royal” hypaspists.
Taphoi wrote: In fact the only other unit involved in the particular action here is the hetairoi, so it is not necessary to envisage vast numbers
Yet Arrian feels disposed to elucidate:
…half of them were to leap from their horses, and to fight as foot-soldiers, being mingled with the cavalry.
We are talking in terms of hundreds (at minimum) I’d imagine rather than tens as “half” of them are to fight “amongst the cavalry”. That would, to me, indicate that the “bodyguards” are not normally “cavalry” – the “companions” are though.
I would also take this view of the below line from Arrian:
Arr. 4.3.2
…he took the body-guards, the shield-bearing guards, the archers, and Agrianians…
To the last...
Arr. 4.30.3
He remained quiet until they began their retreat; then taking ‘700 of the body-guards and shield-bearing infantry…
Your suggestion has some merit. It presupposes the classic “scribal error” though. Whereas this is not impossible it is not necessarily probable. There is no compelling reason to suppose an error based on chiliarchy. We hear (in other sources) of “500 argyraspids” standing guard. It is not to be presumed that Alexander always took, at a minimum, a chiliarchy of hypaspists.
As it stands, there is no reason to number the hypapspists unless that number was less than a “unit” or chiliarchy. Equally there is no reason to number “the seven”.
3.17.2 is, I'd agree, a little more ambiguous. I'd need to see the Latinsed Greek to happy discussing it.
There are other indications in Arrian that his understanding of the difference between the
somatophylakes or “royal” hypaspists and the hypaspists (as used, presumably, by Ptolemy) is flawed. The siege of Tyre is one such:
The shield-bearing guards occupied one of these vessels, which he had put under the command of Admetus; and the other was occupied by the regiment of Coenus, the so called aesthetairoi. Alexander himself, with the shield-bearing guards...
Say again? All 3,000 of them? Unlikely. What is clearly meant here are the royal hypaspists who also appear as hetairoi on the wall.
Again, we’ve been down this path before and we both have firm views. I doubt either of us are likely to change those views. We are, as I noted earlier, debating terms used by a writer (Arrian in this case) well after the events. I do appreciate the manner in which the discussion has taken place though.