Mainz is situated in the Western Germany (Rheinland-Pfalz). During a long time (until 1803) it was an independent state as a archbishopic. Archbishops of Mainz took part in a German policy and social life. Mainz had own coins as an independent state. It"s rather rare coins and I have only one piece: 20 kreuzer 1768, silver, archbishop Emerich Joseph von Braidbach.
Interesting piece - and you have one more from Mainz than I do. By the way, Mainz was not only an independent state or country, its ruler - the archbishop - was also one of the seven (later eight or nine) prince electors. In other words, in the times of the Holy Roman Empire (until 1806) he was one of very few who would elect the king of the HRE. Today Mainz is the state capital of RP, and also the seat of a Catholic diocese ... Christian
