The Mainz Merlon Mystery

[Rafal]

In Medieval Latin, the name was shortened in the 6th century and henceforth written and pronounced “Moguntia” or “Magantia.” In the 7th century, the city name changed to “Mogancia,” “Magancia urbis,” or “Maguntia,” and in the 8th century to “Magontia.” In the 11th century, the name had returned to ‘Moguntiacum’ or “Moguntie.” In general, the city's name was often influenced not by actual linguistic development, but by the prevailing “fashion” of pronunciation. In the 12th century, the city was referred to as “Magonta,” “Maguntia,” “Magontie,” and “Maguntiam.”

I have nothing clever to add so I'll tell you an useless anecdote 
Did you know that in Polish language a lot of names of German towns are in its Latin form? I'm not sure but it can be the only language that does it this way.
So Meinz is Moguncja in modern Polish. There is also Monachium, Norymberga, Koblencja, Brema, Wormacja, Akwizgran, Kilonia, Getynga and some other. 

It's sometimes a source of confusion but may help you to read old Latin chronicles if you are Polish