In the middle of the historical centre of Mainz stands the evangelical Church of St. John, in close proximity to the imposing Romanesque Cathedral of St. Martin. A thousand years ago, construction work on St. Martin’s had not been completed. At the same time, the Church of St. John had already been the seat and official church of the bishops of Mainz for several centuries. It has thus been witness to the centuries-old European history and stands as a stone monument to the dramatic and erratic course of the past.

Archaeological investigations have now been ongoing for some time in the evangelical Church of St. John and these will hopefully answer questions concerning the structural and functional history of the church. The beginnings of the material research of the structural genesis of St. John's dates back to the first decade of the 20th century. At that time, the basic principles of architectonic development had already been clarified. In 2010, during façade restoration work, evidence of older buildings became visible. Since 2013, extensive fieldwork has been conducted in the interior of the church. The historic fabric of the church has revealed new evidence of previous structures, some of which probably date back to the first millennium AD and were at least 15 metres high. A few early graves, as well as a large number of post-medieval burials, are proof of the ecclesiastical function of the architecture. The current appearance of the church is based on these early medieval structures – an extremely rare factum north of the Alps. Equally old as the archaeological research, is the assumption that St. John was the original Sedes or Episcopal Church, which was the bishop's church of Boniface and Rhabanus Maurus. Indeed, both of these bishops provided impetus for a European identity.