The Battle of al-Qādisiyyah, fought in 636, is the decisive engagement between the Arab Muslim army and the Sassanid Persian army during the first period of Muslim expansion.

It results in the Islamic conquest of Persia and is key to the conquest of Iraq.

The battle also sees the alleged alliance of Emperor Yazdegerd III with Byzantine Emperor Heraclius, who marries his granddaughter Manyanh to Yazdegerd as a symbol of alliance.