John Cassian (also John of Masilia); born about 360 C.E. in the Roman province of Scythia (Dobruja); died about 435 C.E. in Masilia (Marseille). As a young man, John Cassian made a pilgrimage to Palestine, where he first came into contact with Christian monasticism in a monastery in Bethlehem. From there, he went to Egypt for over ten years, where he learned the ways of the so-called Anchorite hermits and the ways of the Cenobites, a form of communal monastic living.
Around 400 C.E., John Cassian became a student of John Chrysostom, the Patriarch of Constantinople, who ordained him a deacon. After Chrysostom was banished for the second time, Cassian traveled to Rome, where he spoke successfully to Pope Innocent I on behalf of Chrysostom and was ordained as a priest.
In 415, he founded the monastery of Saint Victor and the cloister of Saint Salvador near Masilia (Marseille); he remained abbot there until his death. He took it upon himself to acculturate Eastern monasticism to the West with certain changes and moderations. He then composed a number of works which had a great influence on the development of Western monasticism.
Among his most important pieces are "De institutis coenobiorum" (419-426), a description of oriental monasticism, and "Collationes patrum Sceticorum" (after 420), fictional dialogues with an Egyptian Anchorite on monkish questions.
John Cassian is considered one of the founders of so-called Semipelagianism, a direction of theological teaching which criticized the teachings of St. Augustine on predestination and grace. Cassian stressed the universality of grace which saved, unlike in Augustine only some souls, but rather all souls.
Toward the end of his life at the request of Pope Leo I, John Cassian composed "De incarnatione domini contra Nestorium" against the Patriarch Nestorius of Constantinople, which is the only Western contribution to the Nestorian controversy.