Salvete omnes,
Since Marius is courteously delaying his travels until others can accompany him, I've decided to go ahead and ask this question that's been bubbling in my mind for some time...
I'm currently writing a book set neither in the realms of alternative history or of fantasy, but somewhere between the two. It's based effectively on the existence of several different cultures, including those of Imperial Rome and 5th century (BC) Athens, and their survival to medieval times. This happens without the intervention of the various tribal movements that happened historically. I understand that this doesn't seem historically possible, but bear in mind this is set in an alternative world with various hypothetical cultures based on these (and other) such cultures.
My question is this: how would you envision the evolution of the Roman army to medieval times? How would it cope with threats such as the Mongolian horse archer (which they already faced to a certain extent in Parthia, of course), the Eastern European lancer, the French cavalier? How would their fortifications evolve to defend against the trebuchet? What tactical innovations would be made?
Also, if our resident hoplite is around, the same question applies for the Greek hoplites and their evolution.
It may seem like an irrelevant question, but it's important to the writing of my book, and, although I've been considering the question quite a lot, I don't have the expertise to be confident in my ideas. I'd therefore be very interested to see what y'all think!
Bene valete,
Curio.