نهر ديالى
The first irrigation works along the Diyala River were undertaken in Parthian times. Indeed, it may be that the lower part of the Nahrawan Canal was originally the lower course of the Diyala. The large-scale canal system of early medieval times however was created in the reign of the Sassanid ruler Khosrau I (), who also established it as a separate administrative district ("Bazidjan Khusraw"). A treasury and mint were possibly established there.