By the mid-9th century, Abbasid authority had eroded and the Tayy were left dominant in the southern Syrian Desert and Jabal Tayy. Under their Jarrahid chieftains, they established themselves in Palestine under Fatimid rule. As the virtually independent rulers of the area between al-Ramla and Jabal Tayy, they controlled the key routes between Egypt, Syria, Arabia and Iraq. They vacillated between the Fatimids and the Byzantines and then between the Seljuks and Crusaders until the late 12th and early 13th centuries, when the Tayy's various subbranches, chief among them the Al Fadl, were left as the last politically influential Arab tribe in the region extending from Najd northward to Upper Mesopotamia.