Lower Manhattan's historic Castle Clinton has a storied history, from protecting New York City from a British siege to accepting over 8 million immigrants in the 19th century. The fort was built between 1808 and 1811 in anticipation of the War of 1812, protruding 200 feet out from the Battery atop an artificial island that was connected by a footbridge.

Initially known as "West Battery" it was intended to complement the East Battery (Castle Williams) on Governors Island, along with Fort Wood on Bedloe's Island (today's Liberty Island), and Fort Gibson on Ellis Island. The forts would be credited with deterring a British attack during the war. 

Following the war, the fort was renamed Castle Clinton after Governor DeWitt Clinton. The Army closed the fort in 1821 and leased it to the city who converted it to "Castle Garden", a popular entertainment venue, in 1824. During this time it was significantly expanded with the addition of a second floor, a fountain in the center and an elevated walkway atop the Castle that offered harbor vistas. Still connected to Battery Park by a small bridge, Castle Garden was used as a theater, ballroom, restaurant, and even beer garden, becoming the largest public assembly hall and entertainment center in the country with seating for 6,000!

During this time immigrants who landed in New York arrived onto various docks, usually at the South Street Seaport. As the influx of immigrants to New York greatly expanded, reaching an all-time high in the 1850s, Castle Clinton was converted to the Emigrant Landing Depot, New York State's first immigrant processing center, in 1855. During the conversion, the site was absorbed by landfill, incorporated into the mainland of Battery Park and Manhattan Island. The State Depot welcomed over 8 million immigrants until 1890 when the Federal Government took control and opened the expanded and isolated Ellis Island facility in 1892, allowing for quarantine of immigrants suspected of carrying disease. Between 1855 to 1892 Castle Clinton processed two-thirds of all immigrants entering the country. 

After its closing, Castle Garden was converted to the New York City Aquarium, which received over 2.5 million visitors a year! During this time, architects McKim, Mead & White severely altered the castle, adding several stories to the masonry fort's original structure. Although it was the city's most popular attraction, in 1941 master planner and Parks Commissioner Robert Moses proposed tearing down the structure to make way for the off-ramp of his Brooklyn Battery Bridge. Moses successfully moved the Aquarium to Coney Island but was forced to build a tunnel instead of a bridge - leaving the Castle standing, just feet from the deep trench that would be dug through the park for the tunnel. In 1946 the Castle was designated a national monument and later rehabilitated back to its original appearance in the 70s. 

Today Castle Clinton is used for purchasing tickets to the Statue of Liberty and Ellis Island. As The Bowery Boys write, "ticket selling is by far the least exciting job in the fort’s history, a rather banal function for a building that traces its origins to the founding of the United States." 

The National Parks Service which oversees the Castle does have a small exhibit on the site's history, which is easily overlooked due to the long lines of tourists waiting to depart to Liberty Island. Hopefully the future has a more exciting use for this monument to American History!