IPSISTARIANS (Hypisistarians). – A sect of the 4th century widespread in Cappadocia, whose existence even in the 9th century is recalled by Nicephorus, Patriarch of Constantinople (Antithet. adv. Const., 1, 5).
The name derives from the fact that the adherents of the sect claimed to believe in one God, the Most High (ἐν ὑψίστῳ), perhaps in protest against the Trinitarian faith of Nicaea; hence the name ὑψισταριανοί. Their
doctrine was a mixture of Hellenic paganism and Judaism. From the former they took some idolatrous practices, such as the cult of fire and light, though without sacrifices or idols; from Judaism they took some legal observances, such as the sanctification of the Sabbath, and certain dietary precepts, including the distinction between pure and impure, while rejecting circumcision.
They seem identical to the Ispistianoi, mentioned by St. Gregory of Nyssa (Contra Eunomium, 2: PG 45, 482 ff.), who also acknowledged only one God, whom they called the Most High or Pantocrator, but not Father. The Ipsistarians recall in some ways the Messalians or Euchites described by Epiphanius (Haer., 80), the Theosebeis recalled by St. Cyril of Alexandria (De adoratione in spir. et veritate, 3: PG 68, 282), and the Caelicolae of Africa, mentioned by St. Augustine (Ep., 44, cap. 6, n. 13: PL 33, 180).
Since information is scarce, historians of religion do not agree on the nature of the Ipsistarians. While Ullmann considers them an eclectic sect combining elements of Judaism and Hellenism, Böhmer instead sees them as a remnant of Sabbatarianism.