Think of free cities as autonomous city states, representing new sociopolitical entities growing out of collapsing ancien regimes. Actually, numerous microstates in Europe (Holy Roman Empire, to be precise) used to have 'Free City' titles in their official names: Basel, Cologne, Strasbourg, Frankfurt, Hamburg, to name a few. They all but dissapeared after unification of Germany by Prussia and the last free city in history has been interbellum Gdańsk (Danzig).It exists. It is called Free Cities--an ironic game given that it is all about slavery.