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 Al-Jazira who mustered up a large army and marched against Emesa, Abu Ubayda's headquarters. Abu Ubayda withdrew all his forces from northern Syria to Emesa, and the Christian Arabs laid siege to the city. Khalid was in favour of an open battle outside the fort, but Abu Ubayda rather sent the matter to Umar, who handled it brilliantly. Umar sent detachments of the Muslim army from Iraq to invade Al-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 at the head of 1,000 men. The Christian Arabs, when they received the news of the Muslim invasion of their homeland, abandoned the siege and hastily withdrew to Al-Jazira. At this point Khalid and his mobile guard came out of the fort and devastated the army, attacking them from the rear. Campaigns in Armenia and Anatolia After the battle Umar ordered the conquest of Al-Jazira, which was completed by late summer 638 A.D. Following the victory, Abu Ubayda sent Khalid and Iyad ibn Ghanm (conqueror of Al-Jazira) to invade the Byzantine territory north of Al-Jazira. They marched independently and captured Edessa, Amida (Diyarbakır), Malatya and whole of Armenia up to Ararat and raided northern and central Anatolia. Heraclius has already abandoned all the forts between Antioch and Tartus to create a buffer zone or no man's land between Muslim controlled areas and mainland Anatolia. Umar for the time being stopped his armies from further invasion deeper into Anatolia but rather ordered Abu Ubayda, now the governor of Syria, to consolidate his rule in Syria. At this point, Umar is reported to have said: Due to the dismissal of Khalid from the army and a famine and plague the next year, the Muslim armies were kept from invading Anatolia. The expedition to Anatolia and Armenia marked the end of the military career of Khalid. Relief efforts during the 638 famine Later that year Arabia fell into a severe drought, and large sums of people began to perish from hunger and epidemic diseases alike, both resulting from the drought and its