There are a growing number of autonomous or semi-autonomous cities. Monaco, Singapore, and the Vatican have been joined by others, notably Koenigsberg in Europe, Montreal in North America, much of Luna, the Islandia space colony, and Port Lowell on Mars. They generally rely on the good will of a powerful neighbor, who accepts the city's autonomy in exchange for benefits its proximity brings. Free cities often compartmentalize useful activities that might be socially destabilizing if applied over a large area, but which would lead to black markets or crime if no outlet were provided for them. Thus, free cities serve as memetic safety valves: tax havens, free enterprise zones in socialist societies, socialist zones in capitalist societies, data havens, religious centers, 'sin cities', or enclaves for unregulated technology. They often act as neutral ground; e.g., Singapore is a meeting place between the TSA, PRA, and China, where they can transact business efficiently, without the necessity for ideological posturing.