It was re-taken by the Byzantines after 1018 , and became part of the newly established Theme of Bulgaria .
The region was absorbed into the Bulgarian Empire in the 850s , where Christianity and a Byzantine - Slavic culture was cemented in the region .
It was re-taken by the Byzantine after 1018 , and became part of the newly established Theme of Bulgaria .
The region was absorbed into the Bulgarian Empire in the 850s , where Christianity and a Byzantine - Slavic culture was cemented in the region .