Castle Clinton was built between 1808 and 1811 to defend the city’s harbor from a British invasion. (The cannons actually were never once fired for defence; shots only rang out for training purposes and celebrations.) In 1940, the circular fort became an opera house and was renamed Castle Garden. It then became New York City’s first immigration center from 1855 to1890. Ellis Island opened in 1892, and the Castle Clinton building underwent yet another change- it became the New York City Aquarium from 1896-1941.
Today Castle Clinton houses exhibits which display the many changes the site has undergone throughout history, as well as a bookstore. It also hosts an annual concert series.