Ardashīr I (flourished 3rd century) was the founder of the Sāsānian empire in ancient Persia (reigned ad 224–241).
Ardashīr was the son of Bābak, who was the son or descendant of Sāsān and was a vassal of the chief petty king in Persis, Gochihr. After Bābak got Ardashīr the military post of argabad in the town of Dārābgerd (near modern Darab, Iran), Ardashīr extended his control over several neighbouring cities. Meanwhile, Bābak had slain Gochihr and taken the title of king. Although Bābak’s request that the Parthian king Artabanus V allow him to transmit the crown to his eldest son, Shāpūr, was refused, Shāpūr nevertheless succeeded him. In the ensuing struggle between him and Ardashīr, Shāpūr was killed, and Ardashīr was crowned king of Persis in 208. Having suppressed a revolt in Dārābgerd, he gradually conquered the neighbouring province of Kermān and the coastal Persian Gulf lands. He made his capital at Gūr (modern Fīrūzābād), which he renamed Ardashīr-Kwarrah.
Ardashīr then moved against western Iran, taking Eṣfahān, Kerman, Elymais, and Mesene. Withdrawing again to Persis, he met the Parthian army at Hormizdagān (site unknown) in ad 224 and won a decisive victory, slaying Artabanus. Soon after, Ardashīr entered the Parthian capital of Ctesiphon, in Mesopotamia, in triumph and was crowned “king of kings of Iran.”
With his son and successor, Shāpūr I, Ardashīr established the Sāsānian empire. Nothing is known of Ardashīr’s personal life; his deeds, however, indicate that he was ruthless, a great soldier, and a capable king. He founded or rebuilt many cities and is credited with digging canals and building bridges. Several great rock carvings commemorate his reign.
Ardashīr made Zoroastrianism the state religion, and he and his priest Tosar are credited with collecting the holy texts and establishing a unified doctrine. Two treatises, The Testament of Ardashīr and The Letter of Tosar, are attributed to them. As patron of the church, Ardashīr appears in Zoroastrian tradition as a sage. As founder of the dynasty, he is celebrated in a 5th-century book in Pahlavi, the Karnamag-i Ardashīr.