15thc perception on swallowtail merlons?

[Pierre Dumont Himself]

This is Mainz in Germany (although some have noted that this could be a generic representation as it reoccurs later, notably in Lyon)

According to my downloads, this image was also used for Bononia (Bologna) and Aquileya (Udine). I haven't figured out which city was originally depicted, though I wouldn't be surprised if it was none of these. 
The view of Venice is similar to the one by Erhard Reuwich (1486).