But at the end of this century the imperial era was rapidly declining and giving way to a new order of things. A fresh period of irruptions from the North was at hand, and within the ancient polity itself a new organisation, the Christian Church, had arisen and was usurping spiritual authority. Milan had been early conspicuous in the history of Christianity. Legend names S. Barnabas himself as the founder and first occupant of her See, and she had testified to the new faith in the days of persecution by the blood of many martyrs. SS. Gervasio and Protasio, the youthful warrior pair, SS. Nazaro and Celso, master and faithful disciple, SS. Felix and Nabor, S. Valeria, San Vittore, and many others, are recorded with picturesque and touching details in Milanese legends and art. And in Milan the triumph of Christianity was first proclaimed, since here Constantine subscribed his edict of toleration in 313. But Christianity, established soon after as the State religion, had yet to struggle with the difficulty of conflicting counsels and doctrines within its own body. The tenets promulgated by the Council of Nicœa in 532 were by no means universally accepted by Christians in the fourth century, and in North Italy the teachings of Arius were widely followed, especially by the Gothic subjects of the Empire. Under the Empress Regent Justina they were the religion of the imperial Court in Milan, and the whole population was divided into fiercely hostile parties by the doctrinal question. It was at this critical point of her political and ecclesiastical destinies that there appeared in Milan one of those epoch-making characters who from time to time arise at moments of hesitation in the history of human communities, and apparently initiate and determine their subsequent course. The great figure of her Bishop Ambrose, Saint and Doctor of the Church, scourge of the Arians, subduer of emperors, stands for Milan at the opening of a new era, to which his dominant mind gives impress, direction and inspiration. From this time forward, Milan is no more the imperial, but the Ambrosian city. Throughout her mediæval existence the consecrating memory of St. Ambrogio, her patron and protector, set like a spiritual jewel in a hundred exquisite and devoutly fantastic legends, is present in her government, her struggles for liberty, her art and peaceful industry, her daily life and the peculiar ritual of her religious worship.