I lost one once, defending Kiev as the Byzantines against the Russians. No magic to it. It was about 1250, I was light on missile troops, most of my infantry were Byz Inf and if they were upgraded it wasn't by much, and I was down about four stars on the general. (I had more or less burgled Kiev from the Russians the turn before because I noticed it was lightly garrisoned, so I hadn't really planned to be fighting the battle).

They didn't do anything clever, just showed up with a load of mega valor Boyars and eventually chewed through all the Byz Inf I had blocking the bridge. Taking archer fire that I couldn't reply to didn't help. Nor did sending some katapractoi round via the other bridge to attacjk the Russians in the rear, but mistiming the attack because they are so **** slow.

Where I went wrong was putting one unit right across the bridge as a plug. That gave me a series of one to one fights between low valour infantry that aren't that good against cavalry, and some jedi cavalry. Dumb. How I won a similar battle a few turns later was leaving the bridge unblocked but forming three units in a square around the exit from the bridge. That has two advantages, first, that any units that come accross get attacked on three sides, (low morale units were coming across the bridge and just routing as soon as they got into the box, without even fighting), and also it means more of your infantry is that bit further out of arrow shot.

The jedi boyars were still tough but that time I got them.