In subsequent ages they extended their conquests into Thrace and Macedonia, and, encamping before the walls of Constantinople, sought to drive the Byzantine emperors into Asia Minor.

In 712, the Bulgarian troops defeated the armies of the Eastern Roman Empire, and laid siege to Constantinople.

Three years later their king concluded a commercial treaty with the Emperor Theodosius III.

which is said to have remained in force for a long time.

In the year 814 the Bulgarians again invaded the Roman Empire, captured Adrianople, and carried a bishop named Manuel, with others of the citizens, into captivity.