In 792 AD the young Basileus Constantine VI led a Byzantine army into difficult terrain to battle the Bulgars near the border fortress of Marcellae. The Bulgar Khan secretly deployed part of his troops behind some hills on the Byzantine left flank, and attacked after they had advanced past them. The Byzantines suffered very heavy losses and lost their baggage train including the imperial tent.
This is a single player scenario with you as the Bulgars.
Edit: This scenario is now available for in-game download.
It's been a while...
kilroy