But in Venice, circa 1600, the areas on the mainland around the lagoon were considered part of Venice in much the same way that the west end or east end or southside are considered part of London even if they are well outside of "The City", or original walled area founded by the Romans.
Not today, of course, since for the most part they are no longer there. Venice has been a shrinking city since about 1750, probably earlier. And it had more to do with economics (the decline of the Venetian Empire as a trade center) than it had to do with industrialization, rising sea levels and the like.
Still don't believe it? Look at exactly the reverse situation in the Netherlands/Belgium. Before 1600, they were colonies of Spain and economic backwaters. Once they became economic trade centers, they reclaimed land from the sea exactly as Venice had done during its peak, albeit with more modern technology.
Sorry, but the Netherlands were at the very center of the European economy from the early Middle Ages on. Most of the great cloth manufacturing centers were there. The axis of the European country was from northern Italy to the Netherlands.
The great wealth of the area was precisely why they were able to fight off the Spanish Empire, the greatest in the world at the time and supported by the looted wealth of Mexico and Peru, for 80 years.
The result of the war was partition of the Netherlands, with the still Spanish-controlled and Catholic segment (later Belgium) indeed becoming an economic backwater for a century or two. While the independent and Protestant section became the wealthiest country on earth for a time.
Charles V, under whom the rift started, was raised in the Netherlands and much more a Netherlander than a Spaniard.
I believe it is generally believed that the land under and around Venice is sinking, largely due to excessive pumping from the fresh water aquifer underlying the area.
As opposed to the sea rising.