Archaeologists Find Athenian Naval Base

[Anomalocaris]

That seems to be the idea although the depth of understanding is questionable.  Also it can't be discounted that some soldiers who served as 'company clerks' for want of a better word may have acted as scribes for their fellow soldiers.  Again, there is a difference even in Latin between the skills needed to write a letter saying "send me some socks" and being able to read and comprehend Frontinus' De Aqueducto, a report on the Roman water supply.

I am under the impression that basic literacy, in the sense of a adaquate vocabulary to understand routine administration and the ability to pronounce words as they are written, was mandated for at least the legionaries, if not the auxiliaries, during the 1st and 2nd century AD.