Assertion: abbasid caliph | /r/HasProperty | abū al-ʿabbās al-saffāḥ
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text: Open revolt in 747, under the leadership of Abū Muslim, led to the defeat of Marwān II, the last Umayyad caliph, at the Battle of the Great Zab River (750) in Mesopotamia and to the proclamation of the first Abbasid caliph, Abū al-ʿAbbās al-Saffāḥ.