Emperor Nikephoros I invaded Bulgaria and sacked the capital of Pliska in 811, but was killed and his army annihilated at the Battle of Varbitsa Pass as he returned to Roman territory.

[1] Khan Krum's peace offer was rejected by Emperor Michael I Rangabe,[1] and the Bulgarians invaded the Roman Empire in the spring of 812.

[2] Krum conquered Develtos and transplanted its population to Bulgaria in June,[2] and seized Adrianople in September 813.

[4] Omurtag later became khan and ordered the execution of all Christians who refused to renounce their faith.

[3] Three hundred and seventy seven Christians were killed, and the following are known by name: An original account of the martyrs was likely made based on the testimonies of prisoners of war released by Bulgaria after the Treaty of 816 in the first half of the 9th century at the Monastery of Stoudios at Constantinople which the menologion and synaxarion are based on.