The Battle of Walaja (Arabic: معركة الولجة) was a battle fought in Mesopotamia (Iraq) in May 633 between the Rashidun Caliphate army under Khalid ibn al-Walid and Al-Muthanna ibn Haritha against the Sassanid Empire and its Arab allies. The Sassanid army is said to have been two times the size of the Muslim army during the battle.