The region is first mentioned in the mid-9th century Life of Saint Gregory of Dekapolis, and designated the area enclosed between the Nestos River in the west, the Rhodope Mountains to the north, the Korpiles defile to the east, and the Aegean Sea to the south. In the early 11th century, it became a distinct administrative unit, but had a chequered history: a dioikesis (fiscal district) in 1047, it is attested as a separate theme—with at least two known banda, Mosynopolis and Peritheorion—in 1083, but most often it is found as part of a composite province along with the older themes of Thessalonica and Strymon.