Something shall first be said concerning the source from which the idea of a Trinity of Persons in the Godhead, thus of three Gods, has proceeded. There are three creeds, called the Apostles', the Nicene and the Athanasian, which specifically teach the Trinity. The Apostles' and the Nicene teach just the Trinity, whilst the Athanasian teaches a Trinity of Persons. These three creeds appear in many of the Books of Worship (Libris Psalmorum); the Apostles' Creed as a psalm which is sung, the Nicene after the Decalogue, and the Athanasian apart by itself. The Apostles' Creed was written after the time of the Apostles. The Nicene Creed was composed at the Council of Nicaea, a city of Bithynia, to which all the bishops in Asia, Africa and Europe were summoned by the Emperor Constantine in the year AD. 325. The Athanasian Creed was composed after that Council by some person or persons in order utterly to overthrow the Arians, and was afterwards received by the churches as oecumenical. From the first two creeds the confession of a Trinity clearly appeared, but from the third or Athanasian Creed proceeded the profession of a Trinity of Persons. That hence arose the idea of three Gods will be seen from what now follows.