Sources: Augustine, City of God; Leo I, Sermons and Letters; Gelasius I, Letters; the Council of Carthage (397 AD); Ambrose of Milan, On the Duties of the Clergy.

The Western Church (~400 AD) consolidates around Rome, Latin theology, and the bishop of Rome’s growing claim to primacy. Key developments: (1) Augustine of Hippo (~354–430 AD) — the most influential theologian in Western Christianity, whose anti-Pelagian writings on original sin, predestination, and grace shape Catholic and Protestant theology alike. His City of God (written after Rome’s sack in 410 AD) reframes the relationship between Christian community and earthly empire; (2) Leo I “the Great” (~440–461 AD) — the first pope to clearly articulate the doctrine of Roman primacy based on Peter’s commission (Matt 16:18–19); his Tome defined the orthodox Christology for Chalcedon (451 AD); he personally negotiated with Attila the Hun (452 AD); (3) The fall of the Western Roman Empire (476 AD) — leaves the papacy as the last functioning institution of Roman authority in the West, enormously strengthening its political role; (4) The Latin Bible — Jerome’s Vulgate (~405 AD) becomes the standard Western text. The Western church’s theological culture — juridical, centered on sin, guilt, satisfaction, and authority — diverges increasingly from the Eastern church’s more mystical, ontological, theosis-centered theology, setting the stage for the 1054 schism.