The ruins of Fortsberg, a typical 18th-century citadel fortress, are located on the summit of a high hill commanding Coral Bay. Ruins of a supporting shore battery, containing five cannon, lie 1,000 feet southeast of the fort. Begun in 1717, Frostberg was the site of a successful slave rebellion on November 23, 1773. Seizing the fort, the liberated African slaves massacred the garrison and occupied most of the plantations on St. John. When two attempts by the Danish authorities failed to suppress the rebellion, 400 French soldiers from Martinique were called in. After six months of fighting, the rebellion was quashed. In 1760, four bastions and a gun deck were added to the fort. During the Napoleonic Wars the fort and adjacent battery were occupied by the British in 1801, and again from 1807 to 1815.
Fortsberg is located on the Fortsberg peninsula of St. John, U.S. Virgin Islands. It is privately owned and not open to the public.