Four men are called the Doctors of the Western Church; St.Ambrose, St.Jerome, St.Augustine, and Pope Gregory the Great.

Few men have surpassed these four in influence on the course of Church history. Of these the first three were contemporaries, while the fourth belonged to a later date.

St.Ambrose determined the ecclesiastical conception of the Church and State;

St.Jerome gave the Western Church its Latin Bible and a great part of the impetus to monasticism;

St.Augustine fixed the theology of the Church until the Reformation;

Gregory the Great (540-604), the first monastic pope, became the founder of the woldly power of the papacy and the secular ruler of the city of Rome.