The fourth century of the Christian era is the golden century of the undivided Church. After the persecution against Christians the Church began, by the Edict of Milan in 313, to organize themselves and also to systematize the truths of faith. Christianity had to meet the challenges of polytheistic religions and philosophies syncretistic, who had doctrinally strong and well trained representants. After the persecution, the Christian Church had no official doctrine of faith or well-defined terminology, which led to a fierce battle in the fourth century, especially for establishing truths of faith. As part of the Roman Empire and Christianity, the South of the Danube was involved in these struggles and theological disputes. Religious life here was very intense, as evidenced by the large number of martyrs, many religious centers that were in this area, and the large number of bishops participating in the Ecumenical Councils of 325 and 381, as well as local councils century IV. Also, Roman emperors in the fourth century, have resided or spent a period of their reign Sirmium, Sardica, Nis and Thessalonica. The Council of Sardica was the first meeting, truly ecumenical Eastern and Western Churches, the bishops of the two regions that have managed to reach a common result.