John Cassian

John Cassian (c. AD 360 – c. 435), also known as John the Ascetic and John Cassian the Roman, was a Christian monk and theologian celebrated in both the Western and Eastern churches for his mystical writings. Cassian is noted for his role in bringing the ideas and practices of early Christian monasticism to the medieval West.

Notable works: De institutis cœnobiorum

Source: Wikipedia — https://en.wikipedia.org/wiki/John_Cassian