fourthcentury

The fourth century (CE) spans roughly 301 to 400 CE and is part of late antiquity. It follows the constitutional and military reforms of the late third century and sees major transitions in politics, religion, and society as the Roman world faced internal reform and external pressure.

Politically, Constantine the Great emerged as the dominant ruler, with sole authority after 324 and the foundation of Constantinople in 330. The century saw continued pressures from Germanic peoples and border tribes, culminating in the Battle of Adrianople in 378, which underscored the vulnerability of the Roman military system. After Theodosius I, who reigned until 395, the empire was permanently divided into eastern and western halves.

Religiously, the century marked the ascent of Christianity. The Edict of Milan in 313 granted toleration, and the First Council of Nicaea in 325 sought doctrinal unity. Theodosius I established Nicene Christianity as the state church and, with subsequent decrees, began suppressing pagan practices, accelerating the Christianization of the empire.

Culturally and socially, Christian theology, monasticism, and ecclesiastical organization grew in influence, while Roman administration and law adapted to a Christianized state. The century laid the groundwork for the medieval Byzantine and Western European worlds, shaping religious and political structures for centuries to come.