Coastal Defense Fort Constitution State Historic Site is located on a peninsula on the northeast corner of New Castle Island. It overlooks both the Pisquatua River and the Atlantic Ocean.
Fort Constitution is one of seven forts built to protect Portsmouth Harbor.
The earliest forts were built to protect the colonists. As Portsmouth Harbor's importance increased with the Revolutionary War shipbuilding industry and the establishment of the Portsmouth Naval Shipyard in 1800, additional fortification was needed. The basic defense concept was to mine the harbor entrances and erect gun batteries. The five remaining forts are obsolete and today considered historic sites or parks which are open to the public. This early fort was followed by a timber blockhouse built in 1666.