 In 721 / 722, the main phase of the war began. In the winter of this year, 30,000 Khazars launched an invasion of Armenia and inflicted a crushing defeat on the mostly Syrian army of the local governor Mi 'laq ibn Saffar al-Bahrani at Marj al-Hijara in February / March 722. In response, Caliph Yazid II (r. 720 – 724) sent one of his most celebrated generals, al-Jarrah ibn Abdallah, with 25,000 Syrian troops north. Al-Jarrah was swiftly successful in driving the Khazars back across the Caucasus, recovered Derbent and even advanced on Balanjar. The Khazars tried to defend their capital by ringing the citadel with a laager of wagons, but the Arabs broke it apart and stormed the city on 21 August 722 or 723. Most of Balanjar's inhabitants were killed or enslaved, but a few managed to flee north. Despite their success, however, the Arabs had not yet defeated the main Khazar army, which like all nomad forces was not dependent on cities for supplies. The continuing threat of the Khazar army forced the Arabs to abandon any attempt to capture Samandar as well, and to retreat to Warthan south of the Caucasus. The sources are obscure on al-Jarrah's activity in 723, but he seems to have led another campaign north (which may indeed be the Balanjar campaign). In response, the Khazars raided south of the Caucasus, but in February 724, al-Jarrah inflicted a crushing defeat on them in a battle between the rivers Cyrus and Araxes that lasted for several days. Al-Jarrah followed up his success by capturing Tiflis and bringing Caucasian Iberia and the lands of the Alans under Muslim suzerainty, becoming the first Muslim commander to campaign through the Darial Pass in the process. This secured the Muslims' own flank against a possible Khazar attack through the Darial, while conversely it gave the Muslim army a second invasion route into Khazar territory.
