After remaining in that community for about three years,[12] they journeyed to the desert of Scete in Egypt, which was rent by Christian struggles. There they visited a number of monastic foundations. 

    Approximately fifteen years later, about 399, Cassian and Germanus fled the Anthropomorphic controversy provoked by Theophilus, Archbishop of Alexandria, with about 300 other Origenist monks. Cassian and Germanus went to Constantinople, where they appealed to the Patriarch of Constantinople, Saint John Chrysostom, for protection. Cassian was ordained a deacon and was made a member of the clergy attached to the Patriarch while the struggles with the imperial family ensued. When the Patriarch was forced into exile from Constantinople in 404, the Latin-speaking Cassian was sent to Rome to plead his cause before Pope Innocent I.[10]

    While he was in Rome, Cassian accepted the invitation to found an Egyptian-style monastery in southern Gaul, near Marseilles. He may also have spent time as a priest in Antioch between 404 and 415. In any case, he arrived in Marseilles around 415. His foundation, the Abbey of St Victor, was a complex of monasteries for both men and women, one of the first such institutes in the West, and served as a model for later monastic development.[13]

       Cassian's achievements and writings influenced St Benedict, who incorporated many of the principles into his monastic rule, and recommended to his own monks that they read the works of Cassian. Since Benedict's rule is still followed by Benedictine, Cistercian, and Trappist monks, John Cassian's thought still exercises influence over the spiritual lives of thousands of men and women in the Latin Church.

    Cassian died in the year 435 in Marseille. He is a saint of the Eastern Orthodox Churches, with a feast day on 29 February, a date assigned also in the liturgical calendar of the Episcopal Church (USA). Because this day occurs only once every four years on leap years, official Church calendars often transfer his feast to another date (usually 28 February).

    The Roman Catholic Church also ranks him as a saint, with a feast day on 23 July. Like his contemporaries Saint Augustine of Hippo and Saint John Chrysostom, he was never formally canonized, a process that came into use several centuries after his death.[13] Pope Urban V referred to him as sanctus (a saint) and he was included in the Gallican Martyrology[14] He is included also in the Roman Martyrology with a feast-day on 23 July.[15] Like the great majority of recognized saints of the Church, he is not one of the saints in the General Roman Catholic calendar of saints for celebration everywhere, but the Archdiocese of Marseilles and some monastic orders celebrate his memorial on his feast day.

      Cassian's relics are kept in an underground chapel in the Monastery of St Victor in Marseilles. His head and right hand are in the main church there."