The siege of Kamacha by the Abbasid Caliphate took place in autumn 766, and involved the siege of the strategically important Byzantine fortress of Kamacha on the eastern bank of the Euphrates river, as well as a large-scale raid across eastern Cappadocia by a part of the Abbasid invasion army. Both enterprises failed, with the siege dragging on into winter before being abandoned and the raiding force being surrounded and heavily defeated by the Byzantines.