Given Mainz's moderately violent history - Romans in punch-ups with the Germanic tribes, French and Prussians at each others throats for years, the Brits pulverising large bits of the city and the Wehrmacht blowing up their own bridges - it's a surprise that there's anything left at all worth looking at.
This is the Bischofsplatz - Bishop's Square. The Bishop's Residence faced this spot from 1802 to 1962 and prior to that, the custodian of the cathedral's art collection from 1666.
And - as from 1962 - a parking structure for the adjacent Karstadt department store. (The protests against the demolition of the damaged structure must have been quite hefty at the time - the history books still mention them)
This gateway is all that remains and was the equivalent of the tradesmens' entrance.
Wouldn't have minded seeing what it looked like from the front...