The Cappadocian Fathers of the 4th century were integral to much of early Christian philosophy. It also produced, among other people, another Patriarch of Constantinople, John of Cappadocia, who held office 517–520. For most of the Byzantine era it remained relatively undisturbed by the conflicts in the area with the Sassanid Empire, but was a vital frontier zone later against the Muslim conquests. From the 7th century, Cappadocia was divided between the Anatolic and Armeniac themes. In the 9th–11th centuries, the region comprised the themes of Charsianon and Cappadocia.
Cappadocia shared an always-changing relationship with neighbouring Armenia, by that time a region of the Empire. The Arab historian Abu Al Faraj asserts the following about Armenian settlers in Sivas, during the 10th century: “Sivas, in Cappadocia, was dominated by the Armenians and their numbers became so many that they became vital members of the imperial armies. These Armenians were used as watch-posts in strong fortresses, taken from the Arabs. They distinguished themselves as experienced infantry soldiers in the imperial army and were constantly fighting with outstanding courage and success by the side of the Romans in other words Byzantine”.As a result of the Byzantine military campaigns and the Seljuk invasion of Armenia, the Armenians spread into Cappadocia and eastward from Cilicia into the mountainous areas of northern Syria and Mesopotamia, and the Armenian Kingdom of Cilicia was eventually formed. This immigration was increased further after the decline of the local imperial power and the establishment of the Crusader States following the Fourth Crusade. To the crusaders, Cappadocia was “terra Hermeniorum,” the land of the Armenians, due to the large number of Armenians settled there.