Defeat at the Battle of Ajnadayn left Syria vulnerable to the Muslim invaders. Khalid decided to capture Damascus, the Byzantine stronghold. In Damascus, Thomas, son-in-law of Byzantine Emperor Heraclius, was in charge. Receiving the intelligence of Khalid's march towards Damascus he prepared the defences of Damascus. He wrote to Emperor Heraclius for reinforcement, who was at Emesa that time. Moreover, Thomas, in order to get more time to prepare for a siege, sent the armies to delay, or if possible, halt Khalid's march to Damascus. One such army was defeated at the Battle of Yaqusa (also known as Waqusa) in mid-August 634 near Lake Tiberias 150 km from Damascus. Another army that halted the Muslim advance to Damascus was defeated in the Battle of Marj al-Saffar on 19 August 634.
Some early writers, including Tabari, appear to have confused this action at Yaqusa with the Battle of Yarmouk, which was fought in the same general area, and have given the year of Yarmuk as 13 Hijri, which is incorrect.