In the early part of this period, Sasanians control most of Mesopotamia, which shares—to the west—an unstable border with Byzantium. In the seventh century, this area is conquered by Arab armies and transformed into the center of Islamic civilization. Under the Abbasid caliphate, the newly founded capital, Baghdad, becomes the cultural and commercial capital of the Islamic world. The distinctive artistic language that develops in Baghdad and Samarra is emulated throughout the realm and greatly influences Islamic art.