Wāsiṭ, military and commercial city of medieval Iraq, especially important during the Umayyad caliphate (661–750). Wāsiṭ was established as a military encampment in 702 on the Tigris River, between Basra and Kūfah, by al-Ḥajjāj, the Umayyad governor of Iraq. He built a palace and the chief mosque and encouraged irrigation and the cultivation of the region surrounding Wāsiṭ. Through its location on the Tigris, at the centre of a network of roads radiating to all parts of Iraq, Wāsiṭ became a great shipbuilding and commercial centre. Even after the caliphal capital was moved from Damascus to Baghdad, the city retained a strategic importance. Only with the shift in the course of the Tigris, sometime in the 15th century, did the city decline and eventually disappear. Thus, an early 17th-century Turkish geographer describes Wāsiṭ as lying in the middle of the desert. Modern scholars are not agreed as to the exact location of the medieval city.