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After an unsuccessful campaign of the Byzantine Emperor Constantine V earlier that year, the Bulgarian Khan Telerig decided to strike back to the southwest and sent a small raiding army of 12,000 to capture Berzitia.
The Byzantine emperor was informed for the raid in due time by his spies in Pliska and gathered an enormous force. Near the town the Byzantines surprised the Bulgarian Army and after a long fight they managed to defeat them due to their much larger superiority in troops.
Constantine V was eager to follow-up his success and led another campaign against the Bulgarians, but once again it failed. However, Telerig learned during this event that all his plans were known to Constantine through a network of spies within his government. He decided to eliminate them once and for all and sent a message to Constantine, stating that he was going to flee in exile to Constantinople. In exchange, Telerig asked the emperor to reveal the spies to his associates in Pliska for their own safety. As Telerig was not the first ruler to flee to Constantinople, Constantine revealed his information and sent the Bulgarian government the list of spies, however Telerig deceived him and did not travel to Constantinople. When Telerig learned of their names he executed them all and eliminated the Byzantine spy network within his government.