 With the devastating defeat at Yarmouk his empire was extremely vulnerable to Muslim invasion. With few military resources left he was no longer in a position to attempt a military come back in Syria. To gain time for the preparations of the defense of the rest of his empire, Heraclius needed the Muslims occupied in Syria. He sought help of the Christian Arabs of Jazira who mustered up a large army and marched against Emesa, Abu Ubaidah ’ s headquarters. Abu Ubaidah withdrew all his forces from Northern Syria to Emesa, and Christian Arabs laid siege to Emesa. Khalid was in favor of an open battle outside fort, but Abu Ubaidah rather sent the matter to Umar, who brilliantly handled it. Umar sent detachment of Muslim armies from Iraq to invade Jazira, homeland of the invading Christian Arabs, from three different routes. Moreover, another detachment was sent to Emesa from Iraq under Qa ’ qa ibn Amr, a veteran of Yarmouk who was sent to Iraq for the Battle of al-Qādisiyyah. Umar himself marched from Medina ahead of 1,000 men. The Christian Arabs, under this overwhelming response, abandoned the siege and hastily withdrew to Jazira. At this point Khalid and his mobile guard came out of Emesa and devastated their army, attacking them from rear. This was Heraclius' last attempt to achieve a comeback on the Syrian front.
