battle won't end

[caravel]

Sorry to hear that, and yes I've had that problem too and many more either similar or worse. Unfortunately it's a bug in the path finding in the game. It seems to happen a lot during sieges and in woods. If you have some missile units that still have ammo you can move those into position and they should shoot at that unit if it's within range (I expect you've already thought of this).

I have had a similar one during a siege where an enemy unit on the walls was "fighting to the death". The unit was partially stuck inside a tower and wasn't moving so all of the men in that unit could not be killed. I had to end the battle...

I don't know of any other workarounds for this except for to accept victory immediately when prompted and not go to hunt down the routers yourself. This ensures that you will win when you should.