SAINT JOHN CASSIAN THE ROMAN, ABBOT, FULL BODY 6955 St. John Cassian was born during the 4th century. He settled in Scetis and made frequent trips to the Thebiad. Many years later, he travelled to Rome, where he established two monasteries. Cassian’s Institutes served as their rule, and his On the Incarnation is a treatise against Nestorianism. St John Cassian died 433-435 AD.