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

Willigis orders the construction of a new cathedral in the pre-Romanesque Ottonian architecture.

This new and impressive building is to be part of Willigis' vision of Mainz as the "second Rome". (The impressive cathedral, dedicated to Saint Martin, is today predominantly Romanesque in style; later exterior additions over many centuries will result in the appearance of various architectural influences seen today.)