The Battle of the Zab and the end of the Umayyad state

The last Umayyad caliph, Marwan ibn Muhammad, was defeated by the Abbasid army at the Great Zab river near Mosul. The Umayyad state collapsed after some ninety years of rule, and upon its ruins arose the Abbasid state.

Marwan ibn Muhammad — among the bravest and hardest of the Umayyads, nicknamed "the Donkey of the Jazira" for his endurance — set out with the hosts of Syria and the Jazira to meet the advancing Abbasid army under ʿAbdullah ibn ʿAli, uncle of al-Saffah.

The two hosts met on the bank of the Great Zab. The Khurasanis held firm with their ordered ranks and their method of kneeling behind their spears; Marwan's army broke, many drowned in the river, and Marwan fled without pause.

The Abbasids pursued him from the Jazira to Syria and then to Egypt, until he was killed at Busir in its south. With his death the page of the Umayyad state in the East was folded, and ʿAbd al-Rahman al-Dakhil escaped among the Umayyads to found for them a new realm in al-Andalus.