from Ctesiphon to win a victory over the Persians at the Battle of Jalawla. He then laid siege to Jalawla for seven months, ending in the city's capture. Then, Abdullah ibn Muta'am marched against Tikrit and captured the city with the help of Christians, after fierce resistance. He next sent an army to Mosul which surrendered on the condition of paying Jizya. With victory at Jalawla and occupation of the Tikrit-Mosul region, the whole of Mesopotamia was under Muslim control. Thereafter, a Muslim force under Qa'qa marched in pursuit of the escaping Persians at Khaniqeen, 25 kilometres (15 mi) from Jalawla on the road to Iran, still under the command of Mihran. Qa'qa defeated the Persian forces in the Battle of Khaniqeen and captured the city. The Persians then withdrew to Hulwan. Qa'qa followed and laid siege to the city, which was captured in January 638. Qa'qa sought permission to operate deeper in Persia, but Umar rejected the proposal, writing in response: Persian raids in Mesopotamia (638–641) By February 638 there was a lull in the fighting on the Persian front. The Suwad, the Tigris valley, and the Euphrates valley were now under complete Muslim control. The Persians had withdrawn to Persia proper, east of the Zagros mountains. The Persians continued raiding Mesopotamia, which remained politically unstable. It seemed the Zagros range was the dividing line between the Rashidun Caliphate and the Sassanids. In the latter part of 638, Hormuzan, who was one of the seven great chiefs of Persia, and had commanded a corps at the Battle of Qadisiyyah, intensified his raids in Mesopotamia. Saad, on Umar's instructions, attacked Hormuzan, while Utbah ibn Ghazwan, aided by Nouman ibn Muqarin, attacked Ahvaz and forced Hormuzan into a peace treaty, under which Ahvaz would remain in Hormuzan's possession as a Muslim vassal state and would pay tribute. Hormuzan broke the treaty, leading Umar to send Abu Musa Ashaari, governor of Busra, to deal with him. After another defeat, Hormuzan signed another treaty on similar terms to the last. This peace also proved short-lived once Hormuzan was reinforced by fresh Persian troops sent by Emperor Yazdgerd III in late 640. The troops concentrated at Tuster, north of Ahvaz. Umar sent the Governor of Kufa, Ammar ibn Yasir, the governor of Busra, Abu Musa, and Nouman ibn Muqarin there, where Hormuzan was defeated, captured and sent to Umar in Medina. Hormuzan apparently converted