 In order to check the Arab advance and to recover lost territory, Emperor Heraclius had sent a massive expedition to the Levant in May 636. As the Byzantine army approached, the Arabs tactically withdrew from Syria and regrouped all their forces at the Yarmouk plains close to Arabia where, after being reinforced, they defeated the numerically superior Byzantine army. The battle is considered to be one of Khalid ibn al-Walid's greatest military victories. It cemented his reputation as one of the greatest tacticians and cavalry commanders in history.
