Six red sandstone towers rise over the square from St Martin's Cathedral, begun under Archbishop Willigis in the late tenth century and rebuilt so often that Romanesque, Gothic and Baroque all have their say in it. The Domplatz was the city's market long before it was anything else, and it keeps that character — traders in the morning, and, on summer evenings, an audience assembled in front of the cathedral for open-air concerts and staged opera on a scale no room in Mainz could take.