How many castles do you need?

[Musashi]

Heh, I'm playing Byzantium and I've managed nicely with only one castle (Corinth) for ages... I managed to take everything from Vienna, Zagreb, and Ragusa in the west, to Trebizond in the east before I finally got another castle (Because the turks begged for a ceasefire and I agreed on the condition they give me Caesarea, so I just left it as a castle).

I even made Venice a vassal.. And then took Bologna from the backstabbing HRE and gave it to the Venetians, since they were down to their last province when they finally accepted vassalage.

I just did a lot of combining units and only a little retraining. Plus I used spears from my cities, and those took most of the casualties.