3 – The Second Battle of Marcellae (792)
While Bulgarian strength was undermined during the reign of Constantine V (741 – 775), it started to recover in the final part of the 8th century at a time when the Byzantine Empire was in a period of turmoil. The Bulgarians invaded Byzantine territory in the valley of the Struma River and defeated their enemies in 789. Emperor Constantine VI tried to alleviate the threat by launching a campaign in Northern Thrace two years later but had to retreat.
However, he began another campaign in 792 and led his army north until they met a Bulgarian army at Marcellae under the leadership of Khan Kardam. Initially, Constantine did not want to engage the enemy in an open battle. However, according to a Byzantine chronicler named Theophanes the Confessor, he was convinced to fight by false astrologists. Apparently, he was told that the stars predicted a victory, so he attacked.
It seems as if the stars failed to tell him that Kardem had hidden part of his cavalry behind the hills overlooking Marcellae. The difficult terrain meant the Byzantine army was unable to stay in shape. Kardem saw this and ordered a counterattack which seriously damaged the enemy army. The hidden cavalry sprang into action and prevented the Byzantines from returning to Marcellae’s fort or their supplies. The Bulgarians inflicted heavy losses on the enemy and chased Constantine VI from the field.
Constantine VI agreed to pay tribute to the Bulgarians but stopped the annual payment in 796 which led to another war. Constantine was overthrown by his mother Irene in the following year while Kardem was probably murdered sometime between 796 and 802. Under the leadership of Khan Krum, the Bulgarian Empire grew stronger, and it inflicted a number of notable defeats on the Byzantines including at the Battle of Pliska in 811.