Northern Forts
In the early days of the American republic (and, perhaps, even in aboriginal days), the high bluffs in northern part of Central Park were the location of significant military activity and construction. As one of the highest points in Manhattan, the tops of these hills made it possible to see and attack invaders coming down the Hudson River, from north of the city and from Long Island.
Following a British attack on Stonington, Connecticut on August 9, 1814, during the War of 1812, General Joseph Swift organized volunteers to quickly build a chain of fortifications across Manhattan for the defense of Harlem Heights. Around 1,600 NY State militia spent the fall of 1814 in these fortifications, but the British never attacked New York City and the war officially ended in December of 1814. None of these fortifications ever saw combat and they were decommissioned and/or repurposed long before construction of Central Park began in 1858.