Emperor Heraclius

In 636 AD, the armies of Islam under the Rashidun Caliphate, defeated the forces of the Byzantine Empire at the Battle of Yarmouk (near the Yarmouk River, along what today are the borders of Syria–Jordan and Syria–Israel, east of the Sea of Galilee). Realizing that the situation was dire, an order was issued by Heraclius, Emperor of Constantinople, for the remaining forces to immediately evacuate the Levant and reestablish themselves in Asia Minor.