In 755, the long peace between Bulgaria and the Byzantine Empire came to an end. This was mainly because, after significant victories over the Arabs, the Byzantine Emperor Constantine V began to fortify his border with Bulgaria. To this aim he resettled heretics from Armenia and Syria in Thrace. Khan Kormisosh took those actions, and the construction of a new fortress along the border, as a breach of the Treaty of 716, signed by Tervel. The Bulgarian ruler sent envoys to ask for tribute for the new fortresses. After the refusal of the Byzantine Emperor, the Bulgarian army invaded Thrace. Looting everything on their way, the Bulgarians reached the outskirts of Constantinople, where they were engaged and defeated by Byzantine troops.