Centurion Position in Battle

[Renatus]

But might this be a sort of etymological point he's making - that the word derives from the number, but that in fact in his day (1st C BC) there were less than that?

EDIT - I think that might be the case. Varro is talking about the origins of various words used in military parlance

A good point. In my earlier post, I implied that Varro's military experience could tell him what the 'proper' number of soldiers in a century should be. It could equally tell him that the number in practice did not correspond with what his linguistic knowledge led him to believe should be the iustus numerus.