Constantine, recognising the advantage of allying himself with such an organisation, issued in 313 the Edict of Milan, which placed all religions on an equal footing. Furthermore, to set at rest the dissensions which were threatening to disrupt the organisation of the Church, he summoned a council of the representatives of all the great branches of the Church to meet in Nicæa, to decide upon a creed which should be acceptable to all.

For with the growth of the Church, Christianity had become encumbered with doctrines that hardened into dogmas, and by this time a controversy was raging over the rival dogmas upheld by two officers of the Church in Egypt, Athanasius and Arius. Both held that Jesus Christ was the Son of God, but Arius maintained that He had proceeded from the Father and was therefore second to the latter, while Athanasius proclaimed the absolute equality of the Father and the Son. The Council of Nicæa pronounced the latter doctrine to be orthodox and branded the Arian as heresy. The Nicene Creed, in which the orthodox was embodied, was accepted in the West, but in the East, the Arian dogma continued to be held.

Apart, however, from its bearing on this question, the Council of Nicæa was an event of profound importance. This first Œcumenical Council, or Council representative of the whole Christian world, not only was an object lesson of the widespread power of the Church, but also exalted the clergy to a high position of spiritual authority amid the temporal distractions of the time.

Constantine, upon his deathbed, accepted the Christian faith. Some fifty years later Theodosius made Christianity the sole religion of the state and the pagan temples were closed.

By degrees the spiritual power of the Church was reinforced by the temporal. The beginning of this change is sometimes dated from the act of the Frankish king, Pepin, to whom the Pope appealed to stem the attack of the Lombards, then pushing south from their possessions in Northern Italy and threatening Rome. Pepin drove them back and handed over a considerable slice of territory to the Pope, to swell the so-called “Patrimony of St. Peter.” The latter, from this time on, became a source of increasing wealth, which enabled the Popes to maintain armies and play the part of princes in the world of politics.

Meanwhile, the temporal power of the Western Church, centred in the Papacy, had been helped by Constantine’s removal of the capital of the Empire to Constantinople. Two circumstances contributed to the change. By this time the Senate had lost even the semblance of authority, and the real source of government was in the consent of the armies. Secondly, the frontiers chiefly threatened were the eastern ones. Constantine accordingly selected as the site of a Nova Roma, the ancient Greek city of Byzantium. It, too, had its seven hills, occupying a promontory between the Golden Horn and the Sea of Marmora, a spot defended, as well as beautified, by nature and already an important gateway of commerce, both by sea and land, between Europe and the East. Constantine planned the new city of Constantinople on extensive lines and set an example of magnificent building that was continued by his successors; so that Constantinople continued for a thousand years to be the Eastern bulwark of European civilisation, until it was conquered by the Moslems in 1453.

Among the results of this change of the capital was, firstly, that the Empire gradually separated into East and West; secondly, that Constantinople became the centre of culture, and, as darkness settled down upon the West, the almost sole refuge of learning and the arts. In the beginning Roman architects directed the character of the new city, but even then the artisans who executed the work were either Byzantines or Greeks, attracted to the new city from various parts of Hellas and Asia Minor. In consequence architecture and the other arts gradually became impressed with a new character, which, for convenience’ sake, is styled Byzantine. It represents, in the case of architecture, a mixture of Roman, Greek, and Oriental; and involved, as we shall see, the treatment of old principles in a new spirit of invention.

The change was encouraged by the contact of Byzantium with Eastern and African civilisation. For as the Western Empire declined in power, the Eastern grew; extending its sway in Asia, where it came into conflict with the Parthians and Persians, and along the northern littoral of Africa. The Metropolitan Bishop of Byzantium became to the Eastern Churches what the Metropolitan Bishop of Rome was to the Western; and exercised a spiritual headship over the Coptic Church in Alexandria, the Syrian Church in Antioch, the Nestorian Church in Ctesiphon, and the Armenian in Asia. Over this widely spread area religious art flourished, coloured in each locality by racial influences, all of which influences in a measure reacted upon the capital city of Byzantium.

Meanwhile, in the West, the Church was labouring to reorganise a settled condition of society by assisting the consolidation of authority. A case in point is the welding of the Frankish tribes into some semblance of a nation. By 486 they had found a great leader in Clovis, who led them across the Rhine, conquered the Romans at Soissons, and proceeded to extend his sway over Gaul. To consolidate his power he married Clotilda, a princess of the Burgundian Goths, and accepted her faith of Christianity. It chanced that she professed the orthodox belief, unlike the majority of the Burgundians and the other German tribes at this time in Gaul, who were Arians. Consequently the Roman Church threw the weight of its influence on the side of Clovis and helped him to found a monarchy in France that endured under the title of Merovingian, so called from Merovech, the grandfather of Clovis.

In time the vigour of the Merovingian kings declined, until the actual power was wielded by the steward of the royal household, the Mayor of the Palace. Gradually this office became hereditary in a dynasty of rulers known as Carolingian or Charles Dynasty. The first great Charles was Mayor Charles, surnamed Martel or the Hammer; the last, Charlemagne, or Charles the Great. The former derived his name from the crushing blows he inflicted upon his enemies, particularly the Saracens, the followers of Mohammed, who by this time (732) had replaced the Vandals along the north coast of Africa, conquered the Visigoths in Spain, and were threatening France. Charles met them at Poictiers or Tours, and in a complete victory saved Christianity to Europe.