Adiabene was an ancient kingdom in northern Mesopotamia, corresponding to the northwestern part of ancient Assyria. The size of the kingdom varied over time; initially encompassing an area between the Zab Rivers, it eventually gained control of Nineveh, and starting at least with the rule of Monobazos I (late 1st-century BC), Gordyene became an Adiabenian dependency. It reached its zenith under Izates II, who was granted the district of Nisibis by the Parthian king Artabanus II (r. 12–40) as a reward for helping him regain his throne. Adiabene's eastern borders stopped at the Zagros Mountains, adjacent to the region of Media. Arbela served as the capital of Adiabene.