19 November 636 CE, 150 miles south of present-day Baghdad, the Sassanid Persians were decisively defeated on the fourth day of the Battle of al-Qādisiyyah by the armies of the Rashidun Caliphate during the Arab conquest of Mesopotamia.
On this day in history, 01/27/18. In 661, the Rashidun Caliphate, then the largest empire in history, ends with the death of Ali. The Rashidun Caliphate is succeeded by the Umayyad Caliphate. Now you know. Historical fact, onthisday.com; map of the Caliphate territory, Wikipedia