Cohorts, Cavalry and Whatever Goes

[D B Campbell]

Just Vegetius, as already mentioned.

Not so. Inscriptions demonstrate that legionary cavalrymen belonged to particular centuries. These are probably the centuries in which they were originally enrolled as infantrymen, as no man appears ever to have enlisted as a cavalryman, but had to be promoted. ILS 2325, for example, is the tombstone of Gaius Valerius Proculus, eques legionis XI > Vindicis (i.e. "cavalryman in the Eleventh Legion in Vindex's century"). There is also evidence to show that an officer called the optio equitum ("optio of the cavalrymen") was carried on the books of a particular century, just like the other promoted posts in the century. Meanwhile, the well-known career of Tiberius Claudius Maximus shows a legionary infantryman being promoted into the legionary cavalry, before going on to hold further promoted posts.

As I said earlier, this is fundamentally different from the situation described by Polybius.