 Complete the following phrase:  After withdrawal from Ctesiphon, the Persian armies gathered at Jalawla, a place of strategic importance due to routes leading from here to Mesopotamia, Khurasan and Azerbaijan. The Persian forces at Jalawla were commanded by Mihran. His deputy was Farrukhzad, a brother of Rustam, who had commanded the Persian forces at the Battle of al-Qadisiyyah. Umar decided to deal with Jalawla first, thereby clearing the way to the north, before taking any decisive action against Tikrit and Mosul. Umar appointed Hashim ibn Utbah to take Jalawla and Abdullah ibn Mutaam to conquer Tikrit and Mosul. In April 637, Hashim led 12,000 troops from Ctesiphon to win a victory over the Persians at the 