St. John's Church, consecrated in 911 by Archbishop Hatto I as St. Salvator, had served as the cathedral for the Bishop of Mainz until the appointment of Willigis as Archbishop of Mainz in 975.

Willigis, having become one of the most influential politicians of his time, is between 991 and 994 regent of the empire.

As part of his vision of Mainz as the "second Rome, he has ordered the construction of a new cathedral in the pre-Romanesque Ottonian architecture.

This new and impressive building is to take over the functions of two churches: the old cathedral and St. Alban's, which is the largest church in the area, belonging to a Benedictine Abbey and being the burial ground for the bishops and other nobles, including Fastrada, a spouse of Charlemagne.

Most of the synods and other important meetings are held at St. Alban's Abbey.

The new cathedral consists of a double chancel with two transepts.

The main hall is built in the typical triple-nave "cross" pattern.

Common for this time, no vault is included due to structural obstacles concerning the size of the building.

Six towers rise from the church.

A cloister is enclosed in the structure and a small freestanding church, St. Mary's Church, connected by a colonnade.

Bronze, employed extensively in the Ottonian period, is used in 988 for a pair of massive cast doors for the cathedral.