On the left bank of the Rhine, we have Mainz – cathedral domes and church spires and stuff.
On the other side of the river, we have Mainz-Kastel.
Which gets its infrastructure provided by the facility management in Mainz.
But is actually a suburb of Wiesbaden and has been that way since 1945, when the American, French , Canadians and Brits (not to forget Russia, of course..) divvied the country up into occupation zones.
The French got the west bank of the Rhein (they only left in 1933 and had been sniffing around for the last couple of centuries), the Americans snaffled the other side with all the heavy industry – what was left of it… – and the associated tax revenues.
Mainz keeps harping on about wanting its 3 suburbs – Amöneburg, Kastel and Kostheim – back, but it’s not happening.
Still, everything’s fairly peaceful when you consider what happens in other places (looking at YOU, Middle East…) when folks (looking at YOU, Brits and French..) use geographical features as borders…