St. Maurice's Abbey is built on the ruins of a Roman shrine of the first century BCE to the god Mercury in the Roman staging-post of Agaunum, and first came to prominence as a result of a now disputed account by Saint Eucherius, Bishop of Lyon, who lived from about 380 to about 449).

Eucherius had experienced a revelation that convinced him of the martyrdom of a Roman legion, known as the "Theban Legion", under the leadership of Saint Maurice, around CE 285, in the area where the abbey is located.

The basilica of St. Maurice of Agaunum becomes the church of a monastery in 515 under the patronage of King Sigismund of Burgundy, the first ruler in his dynasty to convert from Arian Christianity to Trinitarian Christianity.

Sigismund had been a student of Avitus of Vienne, the Catholic bishop of Vienne who had converted Sigismund from the Arian faith of his Burgundian forebears.

Sigismund sets up five groups of monks to whom he entrusts the liturgy of the praise of God.