Shared with Poland and Switzerland
I know it must sound odd but Germany has the greatest number of divided citied in the world. The cities shared with Switzerland (Laufenburg and Rheinfelden) were divided due a treaty signed with Napoleon that the Rhine would become the border. Similarly the cities shared with Poland (several, including Goerlitz and Frankfurt an der Oder) are a consequence of the Soviet ruling that the Neisse would become the border. In both cases historical towns became split, something that affected their urban development and maintenance since. It is a phenomenon mostly prevalent in Europe and quite rare outside it.