what about the "evolution" of the roman army?
I also think that a video about hannibal's campaign through the spain , gaul and then italy herself is quite interesting ,then you could add how such a greatcommander was defeated by someone who had learned and used his very own tactics agaisnt him
(take a look at the battle of cannae depicted in ROME tv series
https://www.youtube.com/watch?v=yGHge4FQ8aM and here's battleof zama
https://www.youtube.com/watch?v=ahBq7qrxoMU those might giveyou ideas...:2thumbsup:)