Marwān’s path to the pinnacle of power began on the empire’s harsh frontiers. In 732 he was appointed governor of Armenia and Azerbaijan, replacing Maslama ibn ʿAbd al-Malik. There he became a semi-legendary figure. His rule in the Caucasus began with resolving long-standing problems: the frugal caliph Hishām had for years failed to pay the local garrisons, nearly provoking a revolt by the Armenian nakharars. Showing diplomatic flexibility, Marwān helped Ashot III Bagratuni extract the arrears from Damascus, thereby securing the loyalty of the Armenian cavalry.
It was precisely his Caucasian experience that convinced Marwān that the old Arab military system based on tribal levies had outlived its usefulness. He carried out a radical military reform: introducing a system of regular pay for all soldiers. Command of the army was transferred to professional officers rather than tribal chiefs. In place of cumbersome phalanxes, Marwān created compact, mobile regiments (kurdus) capable of rapid maneuvering in mountainous terrain.
With this new force, in 737 he passed through the “Alan Gates” (the Darial Gorge) and struck a crushing blow against the Khazar Khaganate, reaching regions no Arab commander had previously penetrated.
The death of Hishām and the subsequent murder of al-Walīd II in 744 plunged the caliphate into the maelstrom of civil strife. Marwān II long remained loyal to the lawful authority, but when Damascus fell to the rebel Yazīd III and power then passed to Ibrāhīm, Marwān decided to act.
His march on Damascus was swift. In the battle on the Nahr al-Jarr river, he employed a military ruse: while the main forces pinned down the enemy, a detachment of woodcutters built a bridge that allowed cavalry to strike the flank of Sulaymān ibn Hishām. In December 744 Marwān entered Damascus. Since the heirs of al-Walīd II were no longer alive (they had been killed in prison by supporters of the previous regime), Marwān ibn Muḥammad was proclaimed caliph.
Marwān II assumed power over a world that was falling apart. His position was complicated by the fact that, as leader of the northern tribes (the Qaysites), he alienated the southern groupings (the Kalbites), who had traditionally dominated Syria.
The Kharijites became the gravest threat to the new caliph. In 745 they seized Kufa and Mosul. al-Daḥḥāk ibn Qays assembled an army of 20,000 fighters, joined even by the Umayyad prince Sulaymān ibn Hishām, thoroughly demoralizing the dynasty.
The decisive battle took place near Kafr Tūsā. The fighting was so fierce that the Kharijites broke through to the caliph’s headquarters and toppled his tent. Marwān was forced to flee, but his disciplined regiments trained in the Caucasus did not waver. Under the leadership of the caliph’s son ʿAbdallāh, and with the support of thousands of armed slaves, the Kharijites were encircled and annihilated. Only by the spring of 747 was Iraq temporarily cleared of the rebels.
While Marwān was extinguishing fires in the heartland, the situation in the East became irreversible. In Khurāsān, the interests of two leaders Naṣr ibn Sayyār and al-Kirmānī collided. Into this chaos returned the Kharijite leader al-Ḥārith ibn Surayj. Merv turned into an arena of endless street fighting, where alliances shifted daily and leaders fell one after another.
The Abbasids exploited this power vacuum. In June 747 their preacher Abū Muslim openly raised the black banners.
By 749, Shiʿite and Abbasid supporters had captured Kufa. Abū al-ʿAbbās al-Ṣaffāḥ was proclaimed the new caliph. Marwān II gathered the last forces of Syria and Mesopotamia for a decisive blow.
On January 25, 750, catastrophe struck at the Battle of the Great Zab River. Marwān II suffered a crushing defeat. Hundreds of members of the Umayyad family perished in the river’s waters. The caliph fled through Syria and Palestine to Egypt, hoping to raise a new army there, but he was overtaken and executed in August 750. With the death of Marwān II, Umayyad rule passed to the Abbasids, who would hold the caliphate for the next five centuries.
