Sasanian dynasty (224–651)
Rulers of the last Iranian empire before the coming of Islam. With roots in the province of Fars, they established an empire encompassing the Iranian Plateau, Mesopotamia, and Central Asia in the 3rd century ad when Ardashir I, the founder of the dynasty, defeated Artabanus VI, the last Arsacid king of kings, at the Battle of Hormozgan in 224 ad. In the 3rd century ad the Sasanian Empire expanded and conducted several campaigns against the Roman Empire. In the early 4th century the Romans under Constantine the Great and the Sasanians under Shapur II recognized each other as equal powers. In the 5th century the nomadic movement of the Hephthalites brought several defeats and weakness to the Sasanian empire. With the reforms of Qobad I and Khosrow I, the empire was reinvigorated and was able to secure its borders. In the 7th century ad, Khosrow II fought the last great war of antiquity with the Roman Emperor Heraclius which caused the defeat of the Sasanian empire. The Sasanian empire came to an end with the Arab conquest in the 7th century ad, during the reign of Yazdegerd III.
More than 40 kings and queens ruled the empire, mainly from Ctesiphon in *Mesopotamia. They were responsible for establishing a narrative for Iranian national history, the Xwaday Namag which in the 11th century became the basis of Ferdowsi’s epic poem the Shahnameh (Book of Kings). Iran was first conceived of as Eranshahr, a distinctive territory and culture, by the Sasanians. The Avesta, the sacred text of Zoroastrianism, was first written down in the 4th century ad during the rule of Shapur II and was last codified during the rule of Khosrow I in the 6th century ad.