Two other physical factors tend to limit the city's population. It is impossible to increase the amount of land available for building by reclaiming land from the sea; a new national law governing coastal development thwarts this possibility. Also, because Cádiz is built on a sandspit, it is a costly proposition to sink foundations deep enough to support the high-rise buildings that would allow for a higher population density. As it stands, the city's skyline is not substantially different from in the Middle Ages. A 17th-century watchtower, the Tavira Tower, still commands a panoramic view of the city and the bay despite its relatively modest height. (See below.)