Christianity in the 4th century

Christianity in the 4th century was dominated in its early stage by Constantine the Great and the First Council of Nicaea of 325, which was the beginning of the period of the First seven Ecumenical Councils (325–787), and in its late stage by the Edict of Thessalonica of 380, which made Nicene Christianity the state church of the Roman Empire.

Christian persecutions

With Christianity the dominant faith in some urban centers, Christians accounted for approximately 10% of the Roman population by 300, according to some estimates. Roman Emperor Diocletian launched the bloodiest campaign against Christians that the empire had witnessed. The persecution ended in 311 with the death of Diocletian. The persecution ultimately had not turned the tide on the growth of the religion. Christians had already organized to the point of establishing hierarchies of bishops. In 301 the Kingdom of Armenia became the first nation to adopt Christianity. The Romans followed suit in 380.

4th century

As a means of recording the passage of time, the 4th century (per the Julian calendar and Anno Domini/Common era) was that century which lasted from 301 to 400. In the West, the early part of the century was shaped by Constantine the Great, who became the first Roman emperor to convert to Christianity. Gaining sole reign of the empire, he is also noted for re-establishing a single imperial capital, choosing the site of ancient Byzantium in 330 (over the current capitals, which had effectively been changed by Diocletian's reforms to Milan in the West, and Nicomedeia in the East) to build the city soon called Nova Roma (New Rome); it was later renamed Constantinople in his honor.

The last emperor to control both the eastern and western halves of the empire was Theodosius I. As the century progressed after his death it became increasingly apparent that the empire had changed in many ways since the time of Augustus. The two emperor system originally established by Diocletian in the previous century fell into regular practice, and the east continued to grow in importance as a centre of trade and imperial power, while Rome itself diminished greatly in importance due to its location far from potential trouble spots, like Central Europe and the East. Late in the century Christianity became the official state religion, and the empire's old pagan culture began to disappear. General prosperity was felt throughout this period, but recurring invasions by Germanic tribes plagued the empire from AD 376 onward. These early invasions marked the beginning of the end for the Western Roman Empire.