Emperor Yazdegerd III sought help from his Byzantine counterpart Emperor Heraclius, who married his granddaughter to Yazdegerd III, an old Roman tradition to seal the alliance. Planned to overpower Umar, their common enemy, both emperors started preparations for a massive coordinated counterattack at once on their respected front to crush the threat in Arabia once for good. This alliance resulted in a bloody year of 636 in which Battle of Yarmouk in Syria and Battle of Qadisiyyah in Iraq resulted in decisive Muslim victory.