Located in the Battery at the southern tip of Manhattan, Castle Garden began operating as an immigrant landing depot on August 3, 1855. Prior to that, it had been a military fort, a restaurant, and an opera house.
At first, Castle Garden was operated by New York State, as immigration was then considered a state, not a federal, matter. This was changed with the Immigration Act of 1882, which authorized the Secretary of the Treasury to contract with states for the enforcement of immigration laws. Thus, beginning in 1882, the admission of immigrants at Castle Garden was handled jointly by the state and federal government.
In 1890, the federal government terminated its contract with the New York State Commissioners of Immigration because it wanted to assume control of immigration at the port of New York. As a result, the New York state authorities refused to allow the federal government to use Castle Garden, and it was closed on April 18, 1890. Remodeled once again, it reopened as the New York City Aquarium on December 10, 1896, remaining a popular attraction until closing in 1941. Although almost entirely demolished in that year, a major preservation battle ensued, resulting in the original fort walls being declared a National Monument by an act of Congress in 1946.