Five massive armies were launched in June to recapture Syria. Khalid, having grasped Heraclius' plan, feared that the Muslim armies would become isolated and then destroyed piecemeal. He thus suggested to Abu Ubaidah in a council of war that he consolidate all the Muslim armies at one place to force a decisive battle with the Byzantines. Abu Ubaidah agreed, and concentrated them at Jabiya. This maneuver delivered a decisive blow to Heraclius' plan, since the latter did not wish to engage his troops in open battle with the Muslim light cavalry. From Jabiya, again on Khalid's suggestion, Abu Ubaidah ordered the Muslim troops to withdraw to the Plain of the Yarmouk River, where the cavalry could be used effectively. While the Muslim armies were gathering at Yarmouk, Khalid intercepted and routed the Byzantine advance guard, ensuring a safe path of retreat.