Saint Eustathius of Antioch (born, Side, Pamphylia—died c. 337, possibly in Thrace; feast day: Western Church, July 16; Eastern Church, February 21) was a bishop of Antioch who opposed the followers of the condemned doctrine of Arius at the Council of Nicaea.
Eustathius was bishop of Beroea (c. 320) and became bishop of Antioch shortly before the Council of Nicaea (325). The intrigues of the pro-Arian Bishop Eusebius of Caesarea led to Eustathius’ deposition by a synod at Antioch (327/330) and banishment to Thrace by the Roman emperor Constantine the Great. The resistance of his followers in Antioch created a Eustathian faction (surviving until c. 485) that developed into the Meletian Schism, a split in the Eastern Church over the doctrine of the Trinity.