CASSIANUS, otherwise called JOANNES EREMITA, and JOANNES MASSILIENSIS, a celebrated solitary, and one of the first founders of monastic institutions in western Europe, was probably born about A.D. 360, and is supposed to have died about the year 418. The place of his nativity has been much disputed; but he spent the early part of his life in the monastery of Bethlehem, with his friend Germanus. In company with that monk he visited Egypt, and dwelt for several years among the ascetics of the desert near the banks of the Nile. In 403 he repaired to Constantinople, where he received ordination as deacon from the hands of Chrysostom. Cassianus was afterwards at Rome; and proceeding thence to Marseilles, he there founded two religious societies—a convent for nuns, and the abbey of St Victor, which last is said to have numbered, during his time, 5000 inmates. He was eventually canonized; and a festival in honour of St John Cassian long continued to be celebrated at Marseilles on the 25th of July.
Cassianus left Collations, or conferences of the fathers of the desert; Institutions, in twelve books; and seven books upon the Incarnation. Of these works, which are all written in Latin, various editions have appeared. The most complete and best edition of his collected works is that published at Frankfurt, 1722, folio, and reprinted at Leipzig, 1733, folio. Cassianus is reckoned among the first of the Semi-Pelagians; a sect that was condemned by some synods, and rejected by the church. (See De Joanne Cassiano Massiliensi, &c., Rostochii, 1824, 1825, 4to, by G. F. Wiggers.)