I'm probably not in the right place,as usual,however

Why Roman? I have a BA and most of an MA in Classics,so I know there is lots of info,but why not phalanxes or cavalry?  It's even mentioned that large animals (ie horses) are useful and powerful.  Personal preference is certainly an acceptable answer;I'm just rereading all my JB books- all that I know of (Skin Games is great!!!)- and i am just curious.  Wondered if it was due to the skittishness horses would probably display around furycrafting,or difficulty with precision while mounted or... whatever.  Just asking!  Love Ancient Roman theme,no quarrel there,just nosy,I guess.
   I don't think this is a spoiler.  If you do,please tell me.
Oh,gods,not more letters!!!  It took me 20 tries to register! And I couldn't get sound on my iPad.