ACACIUS, bishop of CAESAREA. — A disciple and, from 340, successor of Eusebius, the historian, in the see of Caesarea in Palestine. In the Arian controversy he did not side with Nicene orthodoxy, but neither did he explicitly and consistently support Arius. At a council held in Constantinople (360), which he himself directed and which was protected by the emperor Constantius II, he succeeded in having adopted the creed of the Council of Rimini, in which the Son of God was proclaimed similar to the Father, while forbidding the use of the terms *ousia* and *hypostasis*. At the Council of Antioch (363) he drew closer to the Nicene faith, admitting that the Son was of similar substance to the Father (ὁμοιος κατὰ οὐσίαν; cf. *Epistola synodalis*, in Mansi, III, 372), opportunistically deferring to the orthodoxy of the emperor Jovian; but he soon reverted to his earlier position under the successor Valens. He died around 366.
From him were named the *Acacians* those who, in the Arian controversy, refused to admit either the consubstantiality of the Son with the Father, as defined by Nicaea, or the substantial similarity upheld by the Semi-Arians, or the dissimilarity affirmed by the Anomoeans, limiting themselves to asserting that the Son was similar to the Father, convinced that in this way they were faithful to the language of Sacred Scripture. They were therefore called *Homoeans* (from the Greek ὁμοιος). St. Jerome (*De Viris illustr.*, 98) and Socrates (*Hist. eccl.*, II, 4) note some of the numerous writings of A., including a biography of his master and predecessor Eusebius, several commentaries on Ecclesiastes, and *Miscellaneous Questions* (ἐμμεικτὰ ζητήματα).