revolted in the region and briefly took control of Anchialos and the neighbouring cities to use their fleet in his attack of Constantinople until he was crushed in 515. In the 5th-6th century it became the seat of an autocephalous archbishopric.
The Slavic and Avar invasion in 584 meant Anchialos was conquered and its fortifications were destroyed. Avar Khagan Bayan turned the city into his residence for a few months and concluded a peace treaty with the Byzantines. At the eve of his campaigns, the emperor Maurice visited the city to oversee reconstruction.
Byzantine and Bulgarian rule
After 681 and the formation of the First Bulgarian Empire to the north Anchialos played an important role in many conflicts between the two empires. In 708 the forces of Justinian II were completely defeated near the fortress by the army of Bulgar Khan Tervel. On 30 June 763 the Bulgars under Telets suffered a defeat by the Byzantine army of Constantine V. On 21 June 766 the same emperor's fleet of 2,600 heavy ships sank en route to Anchialos, where Constantine was waiting, and most soldiers drowned, forcing him to return to Constantinople.
In May 783 Irene undertook a demonstrative campaign across Thrace and restored Anchialos' destroyed fortifications. The city was first conquered by the Bulgarian Empire in 812, under Khan Krum, who settled Slavs and Bulgars in Anchialos. The Byzantines restored their control over the city and the area in 864.
The Battle of Anchialus took place near the city on 20 August 917, and was one of Tsar Simeon the Great's greatest military achievements. Simeon's army routed the considerably larger Byzantine forces under Leo Phocas. Bulgaria retained the city until 971, when the Byzantine Empire reconquered it and held it for two centuries as Bulgaria was subjugated. After the restoration of the Bulgarian state Anchialos changed hands several times until it was captured by the Venetian knights of Amadeus VI, Count
