In 725, the Caliph replaced al-Jarrah with his own brother Maslama, who already held the post of governor of the Jazira. The appointment of Maslama testifies to the importance placed by the Caliph on the Khazar front, for he was one of the most distinguished generals of the Umayyad empire. For the time being, Maslama remained in the Jazira and was more concerned with operations against the Byzantines. In his stead, he sent al-Harith ibn Amr al-Ta'i to the Caucasus front. In 725, al-Harith was engaged in consolidating Muslim authority in Caucasian Albania, campaigning along the Cyrus against the regions of al-Lakz and Khasmadan. He was probably also preoccupied with supervising that year's census. The next year, Barjik launched a major invasion of Albania and Adharbayjan. The Khazars even laid siege to Warthan, during which they employed mangonels. The use of such advanced siege machines shows, according to Blankinship, that the Khazars were "a militarily sophisticated nation, not a mere disorganized pack of barbarians". Al-Harith was able to defeat them on the banks of the Araxes and drive them back north of the river, but the Arabs' position was clearly precarious.