410 (founding of Lérins) – 434 ("Commonitorium") – 502–542 (Caesarius of Arles)

Western monasticism: Lérins, John Cassian, and Vincent of Lérins's "Commonitorium"

John Cassian, having encountered Egyptian monasticism, transmitted its ideas to the Latin West. For Gallic monks he wrote the "Institutes" (modeled on Pachomius) and the "Conferences" (in the spirit of Evagrius Ponticus).

The monastery founded at Lérins in southern Gaul in 410 produced a series of monk-bishops. The most famous of them was Caesarius of Arles (502–542).

In 434 the monk Vincent of Lérins, in his treatise "Commonitorium," formulated the famous rule for defining catholic tradition. It is what has been believed "everywhere, always, and by all" (ubique, semper, ab omnibus). Among other things, Vincent directed this rule against Augustine's doctrine of predestination as an innovation departing from it.