In 792 AD the young Basileus Constantine VI led a Roman army into difficult terrain to battle the Bulgarians near the border fortress of Marcellae. The Bulgarian Khan secretly deployed part of his troops behind some hills on the Roman left flank, and attacked after the Roman troops had advanced past them. The Romans suffered very heavy losses and lost their baggage train including the imperial tent.
There is very little information on this battle. I found a map on wikipedia, but I do not know the source. The numbers are conjecture. The Roman troops on their left flank begin the battle Disrupted to simulate the Bulgarian surprise attack. The Bulgarian player must be aggressive in multiplayer, because the Romans can win this...
https://www.dropbox.com/s/9hzu7brejwbnk ... 4.zip?dl=1
kilroy