SIXTUS II. followed Stephanus I. as bishop of Rome in 257, and suffered martyrdom under Valerian in the following year. He restored the relations with the African and Eastern Churches which had been broken off by his predecessor on the question of heretical baptism. Dionysius succeeded him.

SIXTUS III., bishop of Rome from July 31, 432, to August 18, 440, had Coelestinus I. as his predecessor, and was succeeded by Leo I.