The Battle of Ullais () was fought between the forces of the Rashidun Caliphate and the Sasanian Persian Empire in the middle of May 633 AD in Iraq, and is sometimes referred to as the Battle of Blood River since, as a result of the battle, there were enormous amounts of Persian Sasanian and Arab Christian casualties.
This was now the last of four consecutive battles that were fought between invading Muslims and the Persian army. After each battle the Persians and their allies regrouped and fought again. These battles resulted in the retreat of the Sasanian Persian army from Iraq and its capture by Muslims under the Rashidun Caliphate.
Background
Before taking on the Persians, Khalid ibn al-Walid wrote to Hormuz, the Persian governor of the frontier district of Dast Meisan, saying:
After their defeat at the Battle of Walaja, the Sassanid survivors of the battle who consisted mostly of Christian Arabs fled from the battlefield, crossed the River Khaseef (a tributary of the Euphrates) and moved between it and the Euphrates. Their flight ended at Ullais, about 10 miles from the location of the Battle of Walaja. The Muslims were aware of the presence of hostile Arabs at Ullais but, as they were less numerous and were survivors of Walaja, they never considered them a military threat until they started to regroup and the Muslim commander Khalid ibn Walid was informed about the arrival of more Arab hordes, mainly from the Christian Arab tribe of Bani Bakr. More reinforcements were raised from the Christian Arab tribes in the region between Al-Hirah and Ullais. The Rashidun Caliphate army under Khalid crossed the river Khaseef and approached Ullais frontally. Emperor Ardsheer meanwhile sent orders to Bahman Jaduya to proceed to Ullais and take command of Arab contingents there and stop the Muslims advance at Ullais. Bahman sent his senior general Jaban with the imperial army to Ullais with orders to avoid battle until Bahman Jaduya himself arrived. As Jaban set off with the army, Bahman Jaduya returned to Ctesiphon to discuss certain matters with the Emperor. He arrived at Ctesiphon to find Emperor Ardsheer very ill and remained in attendance on him. By now the Persians and Arabs had realised that the Muslims' objective was Al-Hirah. They decided to fight and defeat the Muslims army. The Christian Arab contingents were under the command of a tribal chief called Abdul-Aswad, who had lost his two sons in the Battle of Walaja against the Muslims and wanted revenge.
The battle
One of the Muslim commanders, Al-Muthanna ibn Haritha, advanced with the light cavalry scouts to the Ullais and informed the Muslim commander-in-chief Khalid ibn Walid of the location of the hostile Arabs. Khalid tried to reach Ullais before the Sasanian army could reinforce them, in order to avoid a battle with an army that would have heavily outnumbered his own; however he failed to do so. In order to deny the Persians time to organize and to coordinate their plans, Khalid decided to fight the battle that very same day.
According to modern geography the battlefield lies 25 miles south-east of the Iraqi city of Najaf, and about 4 miles south-west of modern Ash Shinafiyah.
The Sassanid army and Christian Arabs contingents were camped side by side with the Euphrates to their left, the Khaseef to their right, and the river junction behind them. Muslim commander-in-chief Khalid ibn Walid arrayed his army in battle formation, appointing Adi ibn Hatim (who was a son of the famous Arab Christian leader Hatim At Tai and a former Christian) as commander of the right wing and Asim ibn Umar commander of the left wing. Information of the Rashidun Caliphate army's advance reached Jaban a little before midday. It was mealtime and the Persian soldiers were to take their meal, but the Sasanian troops abstained from food so as to "display their toughness" to the Muslims.
Jaban arranged the Sassanid army in great haste before the Muslims could arrive, appointing the Christian Arabs to form the wings of his army, with the tribal chief Abdul-Aswad commanding the right wing and the tribal chief Abjar commanding the left wing. The center was formed by the Imperial army. The battlefield ran south-east of Ullais between the Euphrates and Khaseef. The Persian army was deployed with its back to Ullais, while in front of it was arrayed the Rashidun Caliphate army. The northern flank of both armies rested on the Euphrates and their southern flank on the river Khaseef, a distance of about 2 miles.