In April 637, the Arabs defeated another Sasanian army at the Battle of Jalula. After this defeat, Yazdegerd fled deeper into Media. He subsequently raised a new army and send it to Nahavand to retake Ctesiphon and prevent any further Muslim advances. The army that Yazdegerd sent seemed such a serious threat that it led Umar to combine the Arab forces of Kufa and Basra under Al-Nu'man ibn Muqrin and send them against the Sasanians with reinforcements from Syria and Oman. The battle is said to have lasted several days. It resulted in major losses on both sides, including the death of al-Nu'man ibn Muqrin and the Iranian generals Mardanshah and Piruz Khosrow. The battle of Nahavand in 642 was the second military disaster for the Sasanians after the battle of al-Qadisiyyah.