The Mainz Merlon Mystery

[N._N.]

The author of the text, Hartmann Schedel, was a medical doctor, humanist, and book collector. He earned a doctorate in medicine in Padua in 1466, then settled in Nuremberg to practice medicine and collect books. According to an inventory done in 1498, Schedel's personal library contained 370 manuscripts and 670 printed books. The author used passages from the classical and medieval works in this collection to compose the text of the chronicle. He borrowed most frequently from another humanist chronicle, the Supplementum Chronicarum by Giacomo Filippo Foresti of Bergamo. It has been estimated that about 90% of the text is pieced together from works on humanities, science, philosophy, and theology, while about 10% of the chronicle is Schedel's original composition.

This approach was basically the standard not only for encyclopedias as MarcoP mentioned, but for scholarship in general for most of the medieval and early modern period. Research was not primarily based on experiments and observation, but on the compilation of authoritative texts. The concept of compilation did not have the negative reputation of copying without one's own contributions. Instead, it was considered a proof of the author's education and understanding of the classics. This only changed in the so-called scientific revolution (which is a difficult concept on its own) in the 16/17th century and even later for what would today be the humanities, social sciences etc. 

Especially in early prints, the re-use of depicitions of cities was extremly common, mainly to save time and money. The woodcuts may have remained with the printer or the artist, which means it might be worth looking into earlier books published by the same people to identify what they were first used for. 
However, in this case, Mainz may just be one of the generic towns created for the Weltchronik. This version digitized from the Staatsbibiliothek München even has a * symbol for each picture which was supposed to be authentic: You are not allowed to view links. Register or Login to view. Basically, this could be used to rule out a number of cities as the original inspiration with some degree of confidence. However, if the picture is just a copy of an older picture or the combination of different features found in Nürnberg or elsewhere, this would lead nowhere.

In any way, what I find interesting about this ist how the use of swallowtail merlons in a depiction of Mainz in 1493 seemed apparently not completely out of place. It might just simply not have mattered to the publishers, but the extent of their use in 15th century German manuscripts is always interesting to me.