Post-Nicene

Chalcedon settled the doctrine but split the church. The Coptic, Ethiopian, Syriac, and Armenian churches reject Chalcedon as too Nestorian and go their own way — they are still going their own way fifteen centuries later. The Byzantine emperors spend the rest of the century trying and failing to reconcile them; Justinian's Three Chapters edict (544) and the Second Council of Constantinople (553) are the high-water mark of that effort.

The bigger story is the collapse of the Western empire and the rise of the monasteries. Rome had already fallen to Alaric in 410. By the late 400s the western provinces are run by Goths, Vandals, and Franks. The bishops are now the only Roman institution still standing in the west — Leo the Great talks Attila the Hun out of sacking Rome in 452. Augustine's vast theological corpus is being sorted, copied, and transmitted by Cassiodorus and Boethius. Benedict of Nursia writes the Rule around 540 that will define western monasticism for the next millennium.