|I don't know how many of you have read this book. It is a story by David Drake in which a Roman legion, defeated by the Parthians is sold into slavery. OOk, sounds normal enough except the slave masters are aliens. They use the legion as a tool for conquering primitive worlds. The aliens are forced to do this by virtue of a set of policies enforced by the interplanetary alliance (or whatnot) that specifies that advanced weapons cannot be used against those without them. The Romans are given treatments which make them unaging, and the medical technology of the aliens is such that short of major nervous system trauma, anything can be repaired. Thus the legion fights on for a very long time. It's a good story for those that a interested.
However, that is not the point of discussion I propose. What I would ask is would it be possible to take a bunch of modern era soldiers and train them to be effective with, say, Roman era tactics an weapons. Or for that matter would be be able to make a more effective muscle power army than a roman legion? For the sake of discussion we'll limit this to infantry.