The theme of Sebaste (Greek θέμα Σεβαστείας ) was a Byzantine theme in the northeastern Cappadocia and Armenia Minor ( now Turkey ). It has 911 decorated and existed until his case to the Seljuk Turks following the Battle of Manzikert in 1071st
Originally the territory of the later part of the theme topic Armeniakon. The new theme was centered around the city of Sebaste (modern Sivas ). It is not mentioned in the sources before the 10th century. In the year 908 Sebasteia first appears as kleisoura (border district ), already 911 it had been raised to the rank of full-fledged theme.
The theme included the Byzantine border regions along the northern course of the Euphrates. With the expansion of the Byzantine territory to the east, it was extended south to Melitene and Samosata Tephrike so that it was identical with the Roman provinces about Armenia Prima, Secunda Armenia and Syria Euphratensis. After the mid-10th century, its territory was reduced again by creating new themes.
In the 10th century it came into the region to a large influx of Armenians, which soon became the majority. After 1019/1021 Sebasteia and the surrounding areas were given as a fief to the Armenian princes Seneqerim John in exchange for the Kingdom Vaspurakan. From 1074, after the Byzantine defeat at the Battle of Manzikert, the Artsruni also ruled the region as an independent ruler until it was conquered by the Seljuk Turks about 1090.