Sermesianoi

They fled in Byzantine region of Macedonia, following a successful revolt against the Avar Khaganate led by the Bulgar noble Kuber, around the year 680.

[1][2] The Sermesianoi were a mixed population, which included the descendants of Roman (Byzantine) Christians, whom the Avars had captured in the Balkan Peninsula and settled in the region of Sirmium.

[7] They had preserved their Roman and Christian traditions, even though their ancestors had been taken to the Avar Khaganate some 60 years prior to Kuber's appointment.

[5][10] The emperor gave his consent and ordered the nearby Slavic tribe of the Dragovites to supply Kuber and his people with food.

[5][6] Kuber and his associate Mauros subsequently attempted to seize Thessaloniki, taking advantage of a civil war in the city but were unsuccessful.