Built to keep people out; now welcomes millions in. Located at the southern tip of Manhattan Island, Castle Clinton stands where New York City began, and represents not only the city's growth, but the growth of a nation. Initially intended to prevent a British invasion in 1812, the fortification has transformed over the years to welcome theatergoers, immigrants, sightseers, and now, millions of visitors to New York Harbor.

...Excerpt from NPS website