They have, look up the warhammer historical books, Warhammer Ancient Battles, Hannibal and the punic wars, Spartacus, Fall of the west, The age of Arthur, and last but not least Byzantium beyond the Golden Gate. All of these deal with specifically the different roman armies through 1000-1200 years of technological and sociological development, as well of course with their various enemies.
These books specifically are why I made the comment "drilled and stubborn"
they also have made a catch all medieval book called the armies of chivalry, which include the Holy roman empire, the italian condottieri states, the teutonic order, The kingdom of poland, Russia, Burgundian ordonnance, Switzerland, French ordonnance, and many others.
No excess fluff you can look in a real history book for that, just lots of lists.