A parallel of sorts -- maybe not a super-close one -- can be seen between London-and-Southwark; and another pair of settlements on either side of a river, much further north. What is now the London Borough of Southwark, was for a good many centuries in every way a different and distinct town, from the City of London just across the bridge over the Thames. If I understand rightly: for a few centuries after that, it was sort-of a part of the City of London, but not completely: playing host to various fun-and-vice establishments not tolerated in the City proper. A geographical parallel with Newcastle and Gateshead, on different sides of the Tyne -- but those two have always been totally different communities in their own right,