informed him about the move, Khalid having received permission from Abu Ubayda, galloped towards Damascus with his mobile guard. While Abu Ubayda fought and defeated the Byzantine army in the Battle of Marj ar-Rum, Khalid moved to Damascus with his cavalry and attacked and defeated Theodras in the second battle of Damascus. A week later, Abu Ubayda himself moved towards Baalbek (Heliopolis), where the great Temple of Jupiter stood. Baalbek surrendered to Muslim rule after little resistance and agreed to pay tribute. Abu Ubayda sent Khalid straight towards Emesa. Emesa and Chalcis sued for peace for a year. Abu Ubayda, accepted the offer and rather than invading the districts of Emesa and Chalcis, he consolidated his rule in conquered land and captured Hama, Maarrat al-Nu'man. The peace treaties were, however, on Heraclius's instructions, to lure the Muslims and to secure time for preparation of defenses of northern Syria (present day Lebanon, Syria and southern Turkey). Having mustered sizeable armies at Antioch, Heraclius sent them to reinforce strategically important areas of northern Syria, like Emesa and Chalcis. With the arrival of Byzantine army in the city, the peace treaty was violated, Abu Ubadiah and Khalid thus marched to Emesa, and a Byzantine army that halted Khalid's advance guard was defeated. The Muslims besieged Emesa which was finally conquered in March 636 after six months of siege. Battle of Yarmouk After capturing Emesa, the Muslims moved north to capture whole of the northern Syria. Khalid, acting as an advance guard took his mobile guard to raid northern Syria. At Shaizer, Khalid intercepted a convoy taking provisions for Chalcis. The prisoners were interrogated and informed him about Emperor Heraclius' ambitious plan to take back Syria. They told him that an army, possibly 200,000 strong, would soon emerge to recapture their territory. Khalid stopped there. After his past experiences, Heraclius, now had been avoiding pitch battles with the Muslims. He planned to send massive reinforcements to all the major cities and isolate the Muslim corps from each other, and thus separately encircle and destroy the Muslim armies. Five massive armies were launched in June 636 to roll back Syria. Khalid, sensing Heraclius's plan, feared that the Muslim armies would be isolated and destroyed. In a council of war he suggested that Abu Ubayda draw all the Muslim armies to one place so as to fight a decisive battle with the Byzantines. As per Khalid's