Fort William and Mary
Fort William and Mary was a colonial defensive post on the island of New Castle, New Hampshire at the mouth of the Piscataqua River estuary. First fortified by the British in 1632, the fort guarded access to the harbor at Portsmouth. On December 14, 1774, a local mob of several hundred anti-British firebrands from the Portsmouth area, led by John Langdon, stormed the post and seized the garrison's powder, which was distributed through several New Hampshire towns for the use of local militias.

1774 raid
Fort William and Mary was the only military post in the Portsmouth area, normally used only to store supplies and for militia training. As tensions increased before the American Revolutionary War, Lord North's ministry had cautioned the colonial governors to secure arms, powder, and shot. Accordingly, in the summer of 1774 Governor John Wentworth installed a small garrison to guard the fort's supplies. On October 19, King George III issued a confidential order forbidding the export of arms and powder to America. Nevertheless, word reached the locals. The port at Boston had been closed since the Boston Tea Party and the city occupied. The Portsmouth Committees of Safety and Correspondence was aware that powder and shot had recently been seized elsewhere, including in Rhode Island. Rumors flew reinforcements from Boston were expected. On December 13, Paul Revere sounded the alarm. The next day, John Langdon made his way through Portsmouth with a drummer, collecting a crowd. About forty men responded to his challenge, setting upon the fort from the sea. A single volley rang from the British, answered by the Colonials, who quickly overwhelmed British Captain Cochran and his garrison of five men without injury. Breaking into the magazine, they removed seventy-two barrels of powder. One day later, additional rebel forces came from throughout the colony. Led by John Sullivan, they surrounded the governor's home, who averted violence by giving in to their demands. That evening, the rebels returned to the fort, removing all of the arms, supplies, and some cannons.

Despite his assurances to the contrary, Governor Wentworth had sent to Boston for help. The forty gun frigate Scarborough arrived on December 19 with one hundred marines. In spite of this, the governor and his family had to take refuge in the fort by the summer of 1775. Finally giving up, the British abandoned the fort and removed any remaining equipment to Boston along with Governor Wentworth. The captured supplies were later used by New Hampshire's forces in the Siege of Boston.

Fort Constitution
The state gave Frost Point, on which Fort William and Mary stood, to the Federal government in 1791 to protect Portsmouth. In 1800, the Portsmouth Naval Shipyard was established upriver on Fernald's Island (now part of Seavey's Island) and the fort was rebuilt. Walls were doubled in height and new brick buildings added. Work was completed in 1808 and the defense renamed Fort Constitution. On July 4, 1809, an accidental explosion marred Independence Day celebrations at the fort, killing a number of soldiers and civilians. During the War of 1812 the fort was manned and expanded, Walbach Tower, a Martello tower, being built in 1814. During the Civil War, Fort Constitution was rebuilt as a three-tiered granite fortress. However, advances in weaponry, particularly armored, steam-powered warships with heavy guns, rendered the masonry design obsolete before it was finished. In 1897, construction began on Battery Farnsworth, located under the hill on which Walbach Tower stands. Named for Brigadier General Elon J. Farnsworth, the installation included two 8-inch breech-loading rifles on disappearing carriages. Given back to the state in 1961, Fort Constitution State Park was listed on the National Register of Historic Places in 1973, and is today open to the public.

The Lighthouse
Since 1771 the fort has been home to a lighthouse. The current installation, the Portsmouth Harbor Light, was completed in 1878. Its Fourth Order Fresnel lens remains a valuable aid to navigation. The tower and the grounds immediately around it are open for scheduled tours.