Monk and ascetic writer, born probably Provence; died probably near Marseilles.
With his friend Germanus he visited the holy places in Palestine and they became monks at Bethlehem.
After several years among the Egyptian solitaries, they came to Constantinople where Cassian became a favorite disciple of Saint John Chrysostom, and in his behalf was sent to Rome, where he is believed to have been ordained.
About 415 he was at Marseilles where he founded two monasteries, one for men and the other for women, introducing in the West the rules of Eastern monasticism.
His two principal works, "" and "," deal with the cenobitic life and the deadly sins.
He wrote against the Nestorians, but originated Semipelagianism which was later condemned.
By some he was regarded as a saint.
New Catholic Dictionary