Castle Clinton is a historic fort located in Battery Park, New York City. Built between 1808 and 1811, it was originally designed to protect the harbor from British attacks during the War of 1812. The fort is circular in shape and made of sandstone, featuring a moat and a series of cannons. In the late 19th century, Castle Clinton was repurposed as an immigration station, welcoming millions of immigrants to the United States. Today, it is a national monument and part of the National Park Service, serving as a reminder of the city's rich history and its role in immigration.