Fort Jay (background: Brooklyn), the oldest defensive structure on the island, is situated on the location of earthworks originally built to defend New York City during the American Revolution. General Israel Putnam constructed the first earthen fortification starting in April 1776, and armed it with eight cannons for the defence of New York Harbor.

Castle Williams with view of Manhattan. A circular fortification of red sandstone on the northwest point of Governors Island, part of a system of forts designed and constructed in the early 19th century to protect New York City from naval attack.