Battle of River According to Arab and Muslim sources , the Battle of River took place in Mesopotamia ( Iraq ) between the forces of the Rashidun Caliphate and the Sasanian Empire . Muslims , under Khalid ibn al - Walid ' s command , defeated the numerically superior Persian army . Prelude . The Prophet Mohammad died on 8 June 632 , and Abu Bakr succeeded him as first Caliph . Abu Bakr ' s Caliphate lasted for 27 months , during which he crushed the rebellion of the Arab tribes throughout Arabia in the successful campaign against apostasy and restore the authority of Madinah over Arabia . Once the rebellions had been put down , Abu Bakr began a war of conquest . He launched campaigns against the Sassanid Empire and the Eastern Roman Empire ( Byzantine Empire ) and thus set in motion a historical trajectory that in just a few short decades would lead to one of the largest empires in history . After the Ridda Wars , a Muslim tribal chief raided the Persian frontier towns in Iraq . After the success of these raids Abu Bakr planned to expand his empire . He started with Iraq , a rich Persian province . After centuries of Persian power and glory , it was important for Abu Bakr ' s expedition to not to suffer a defeat , for that would confirm and strengthen the fear for the Persian military strength . To overcome these concerns he decided that the army that would invade Persia would consist entirely of volunteers . He put in command of the army his best general Khalid ibn al - Walid . Muslims invaded the Sassanid Persian Empire in April 633 and defeated the Sassanid army in the Battle of Chains , where the Marzbān ( provincial governor ) Hormuz was killed by Khalid ibn al - Walid in a duel . Background . Before the Battle of Chains , the Marzbān Hormuz wrote to the emperor about the threat from Arabia and concentrated an army for the battle , consisting of a large number of Christian Arab auxiliaries , and before the battle the emperor sent a big army led by a Top - ranking general by the name of Qarin , his role was to protect Uballa which was an important port of the Persian Empire in case the Muslims defeated Marzbān Hormuz . Battle preparation . Persian preparation . After the Battle of Chains the small force of the Persian army led by the officers commanding the wings Qubaz and Anushjan joined to Karinz ' s army , survivors from the Battle of Chains had informed commanding officers of how Persian veterans had abandoned and joined the Muslim forces allowing the Muslims to fill up lines with experienced Persian veterans who converted to Islam and would face inexperienced conscripts , the idea would lead many to abandon the cause and return home . Karinz panicked and chose to fight out of Uballa in a place called al Madhar , knowing the Persian veterans who had converted to Islam would not know the area . Karinz chose this place because it was near the Euphrates River making it easier for the Persian regulars to arrive with ease . Muslim preparation . Khalid knew that the Persians had organised their army in Al madhar , so he led the army , and sent a small detachment led by Muthana ibn Haris . The aim was to arrive before the Persian forces could gather their strength and strike them whilst weak and unprepared , like most battles this tactic would allow Khalid to exploit and execute many maneuvers before experienced armies could react . When Khalid arrived , he saw Persian ships still arriving at the edge of the river , and immediately understood that the Persian Army was still unprepared and not ready for battle . The Arab aims where to strike before the more experienced veterans would arrive . The battle . Khalid faced the Persians with about 17 , 000 men ; , before the battle , Qarin challenged Khalid bin Walid to a duel , Khalid accepted the challenge but when he moved to face Qarin , Another men called Maakal ibn el acha reached Qarin before Khalid , Maakal was an experienced swordsmen and he killed Qarin , As the Persian commander went down before the sword of Maqal , the other two Persian generals , Qubaz and Anushjan , came forward and gave the challenge for single combat . The challenge was accepted by the commanders of the Muslim wings , Asim and Adi . Asim killed Anushjan . Adi killed Qubaz . As these Persian generals fell , Khalid gave the order for a general attack , and the Muslims rushed forward to assault the massed Persian army , the death of the Persian Commanders was a psychological victory for the Muslims , and Khalid ordered a general attack , According to Tabari , 30 , 000 Persians were killed in this battle . Aftermath . After the Battle of River , Khalid defeated the Persian armies in three more battles ( battle of Walaja – battle of Ullais – battle of Hira ) and captured his objective : Al - Hirah . The first Muslim invasion of Iraq was completed within four months . Abu Bakr didn ' t direct Khalid to move deeper into the Sassanid territory , and after nine months he sent him to command the invasion of Byzantine Empire on the Syrian front .