Diyala River
The Nahrawan Canal () was a major irrigation system of the Sassanid and early Islamic periods in central Iraq, along the eastern banks of the Tigris and the lower course of the Diyala River. Created in the 6th century, it reached its peak under the Abbasid Caliphate, when it served the main water supply for the Abbasid capital of Baghdad, while the regions irrigated by it served as the city's main breadbasket. Its destruction and progressive abandonment from the mid-10th century onwards mirror the Abbasid Caliphate's decline.