The Battle of al-Qādisiyyah, fought in 636, was the decisive engagement between the Arab Muslim army and the Sassanid Persian army during the first period of Muslim expansion.
It resulted in the Islamic conquest of Persia and was key to the conquest of Iraq.
The battle also saw the alleged alliance of Emperor Yazdegerd III with Byzantine Emperor Heraclius, who married his granddaughter Manyanh to Yazdegerd as a symbol of alliance.
The Sassanids fought on to regain control of their lands until 653. With the death in that year of the last Sassanian emperor, Yazdgerd III, the Sassanid Empire collapsed. Persia, now known as Iran, became an Islamic land.