How were officers trained?

[tonyodysseus]

An important document in this regard must be Marius' speech in Sallust's "Jugurthine War" (chapter 85). Just about all of it is relevant but here is particularly comparing his qualifications as a humbly born soldier with those of the great aristocrats.

You have chosen me to conduct the war against Jugurtha, and this has greatly annoyed the nobility. Now consider whether it would be better to alter you decision -- I mean, to appoint for this or for any similar work some member of that coterie of noblemen, a man with a long pedigree and a household of family portraits, but without a single campaign to his credit, who, faced with a serious task which he does not know the first thing about, will get excited and run about trying to find some commoner to instruct him in his duty. This is in fact what generally happens: the man you appoint to take command looks for another to command him. I myself know cases in which a consul, after his election, has taken to studying history and Greek military treatises. This is reversing the natural order of things. For although you cannot discharge the duties of an office until you have been elected to it, the necessary practical experience should come first. Compare me, the "new" man, with these high and mighty ones. What they know only from hearsay or reading, I have seen with my own eyes or done with my own hands. What they have learned out of books, I have learned from the battlefield. It is for you to judge whether words or deeds are more to the point. Etc." (translation of S.A. Handford, Penguin Classics, 117-118).

So apparently sometimes the officers weren't really trained at all.