معركة اليرموك
The Muslim conquest of Syria appeared a significant threat to the Byzantine empire and Heraclius thus ordered Trithyrius to lead an army to counter the attacks. His real role with the army is questionable, but his involvement brought reassurance nonetheless. In August 636, he charged down to the Yarmouk River, an eastern tributary of the Jordan River, to fight the Rashidun army at the Battle of Yarmouk.