Muslim conquest of the Levant
Battle of Marj ar-RumBeqaa Valley, Lebanon
After Byzantine forces are destroyed in Battle of Fahl by Khalid, Rashidun army split their forces to continue the conquest in separate ways. Amr ibn al-Aas and Shurhabil ibn Hasana moved south to capture Palestine, while Abu Ubaidah and Khalid moved north to capture Northern Syria. While the Abu Ubaydah and Khalid were occupied at Fahl, leaving only Yazid ibn Abi Sufyan in Damascus. Heraclius sensing the opportunity to relieve Damascus and immediately sent an army under General Theodore the Patrician to recapture Damascus. Theodore brough a sizable forces of cavalry in this mission. Meanwhile, the caliphate army manage to learn Theodore movements as Abu Ubaydah and Khalid have already defeated the Byzantine in Fahl, they immediately taking a detour to intercept Theodore.
The battle actually consisted of two different battles in separate areas. But since the second battle was attended immediately by Khalid ibn Walid after he has finished the first battle in short span, early Muslim historians regard this conflicts as single conflict.
Rashidun army achieved decisive victory in this battle and all of the Byzantine commander are killed in both battles