(Wikipedia) - The Battle of Marj Ardabil or the Battle of Ardabil was a battle fought on the plains surrounding the city of Ardabil in northwestern Iran in 730 CE. The Khazar army led by Barjik, the son of the Khazar khaghan, invaded the Umayyad provinces of Jibal and Azarbaijan in retaliation for Caliphate attacks on Khazaria during the course of the decades-long Khazar-Arab War of the early 700s.
Barjik's expedition into northern Iran (and later into Kurdistan and northern Mesopotamia) may have been an attempt to establish Khazar rule south of the Caucasus Mountains.
An outnumbered force led by the Umayyad general Al Djarrah Al Hakami engaged the Khazars for three days. Ultimately, abandoned by many of their Mawali auxiliaries, the Caliph forces were overwhelmed and defeated. During the course of the battle, al-Djarrah was killed. The victorious Barjik mounted his head on top of the throne from which he commanded the battles of his Middle Eastern campaign. According to the historian Agapius of Hierapolis, the Arabs suffered 20,000 dead and twice that number were captured; a figure which probably includes the population of Ardabil and the surrounding territories.
Following their victory, the Khazars occupied Ardabil. The next year, however, Barjik led an army to Mosul and was defeated. According to Muhammad ibn Jarir al-Tabari, the Muslims were so enraged by Barjik's desecration of their commander's head that they fought with extra vigor. The Khazar army at Mosul was defeated and withdrew north of the Caucasus Mountains.