Battle of Ullais

The Battle of Ullais (Arabic: معركة أليس) was fought between the forces of the Rashidun Caliphate and the Sassanid 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 Sassanian and Arab Christian casualties.

Battle of Ullais
Part of Muslim conquest of Persia

Overview of the region where the Battle of Ullais was fought, showing the river Euphrates and its tributary the Khaseef (Iraq)
DateMay 633 A.D.
Location
Sasanian Mesopotamia (modern Iraq)
Result Decisive Rashidun Victory
Belligerents
Rashidun Caliphate Sasanian Empire
Arab allies
Commanders and leaders
Khalid ibn al-Walid Jaban
Abdul-Aswad 
Abjar 
Strength
18,000[1] 70,000[dubious ]
Casualties and losses
~2,000 70,000 killed (primary sources)[2][3][4]

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 Sassanid Persian army from Iraq and its capture by Muslims under the Rashidun Caliphate.