Before anyone asks any questions, NO, there is not an end to it. Not yet, at least.
This is a pretty basic map. You have to defend two castles (not under your control) from monstrous hordes of enemies. The south fort is much more at risk than the north, and remember, you are the Teutons, so your infantry can shoot additional arrows as well (since you're in post-imperial). You get reinforcements in the form of elite cataphracts; two every game minute. After ten minutes, you get an additional two every half game minute. (so six every game minute)
Let neither castle fall, and you will be victorious!