In February 813 the Bulgarians raided Thrace but were repelled by the Emperor's forces. Encouraged by this success, Michael I summoned troops from the entire Byzantine Empire and headed north, hoping for a decisive victory. Krum led his army south towards Adrianople and pitched camp near Versinikia. Michael I lined up his army against the Bulgarians, but neither side initiated an attack for two weeks. Finally, on June 22, 813, the Byzantines attacked but were immediately turned to flight. With Krum's cavalry in pursuit, the rout of Michael I was complete, and Krum advanced on Constantinople, which he besieged by land. Discredited, Michael was forced to abdicate and become a monk — the third Byzantine Emperor forced to give up the throne by Krum in as many years.