Castle Garden was the United States' immigration processing depot at the port of New York from 1855 to 1890 and welcomed more than 8 million immigrants before it was closed. The building is "a circular sandstone fort now located in Battery Park at the southern tip of Manhattan Island", and was originally designed as a fort.
More than one in six native-born Americans are descendants of immigrants who entered the United States through Castle Garden. Today, Castle Garden is known as Castle Clinton National Monument.