Venetcia!
For a thousand years it became the fore-runner of capitalist ventures -- a city ruled by contracts and profit. It was so tied to its sea trade and ventures that is was considered more than an isolated city but instead a kingdom of the sea. It was autocratic for much of its lifespan, ruled by an appointed Doge.
On another note, next year is the fictional take-off time for James Blish's "Cities in Flight" written over fifty years ago where Manhattan takes flight to outer space to become an independent entity in space.