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.
Silver ring with Chi Rho symbol found at a 4th century Christian burial site in Late Roman Tongeren, one of the oldest proofs of a Christian community in Belgium, Gallo-Roman Museum (Tongeren)
Emperor Constantine presents a representation of the city of Constantinople as tribute to an enthroned Mary and baby Jesus in this church mosaic. St Sophia, c. 1000.
Icon depicting Emperor Constantine, center, accompanied by the Church Fathers of the 325 First Council of Nicaea, holding the Nicene Creed in its 381 form.
Early manuscript illustration of Council of Constantinople
In the year before the Council of Constantinople in 381, the Trinitarian version of Christianity became the official religion of the Roman Empire when Emperor Theodosius I issued the Edict of Thessalonica in 380, which recognized the catholic orthodoxy of Nicene Christians as the Roman Empire's state religion. Historians refer to the Nicene church associated with emperors in a variety of ways: as the catholic church, the orthodox church, the imperial church, the imperial Roman church, or the Byzantine church, although some of those terms are also used for wider communions extending outside the Roman Empire. The Eastern Orthodox Church, Oriental Orthodoxy, and the Catholic Church all claim to stand in continuity from the Nicene church to which Theodosius granted recognition.
Missorium of Emperor Theodosius I, who declared Nicene Christianity to be the State religion of the Roman Empire. This piece was found in Almendralejo.
The Hagia Sophia basilica in Constantinople, for centuries the largest church building in the world.