Flavian I of Antioch (ca. 320-February 404) was a bishop or Patriarch of Antioch from 381 until his death. He was born about 320, most probably in Antioch. He inherited great wealth, but resolved to devote his riches and his talents to the service of the church. In association with Diodore, afterwards bishop of Tarsus, he supported the Catholic faith (i.e., orthodox Christian) against the Arian heretic Leontius, who had succeeded Eustathius as Patriarch of Antioch. The two friends assembled their adherents outside the city walls for religious services (according to Theodoret, it was in these meetings that the practice of antiphonal singing was first introduced in the services of the church).