Fort Frederik, also known as Frederiksfort, is a U.S National Historic Landmark in Frederiksted, United States Virgin Islands. It was built in the 18th century by the Danish government to protect St. Croix against invasion of pirates, smugglers and European powers. It was the center of the abolition of slavery in the Virgin Islands in 1848. This deep red rubble and masonry fort, and the trapezoidal design is typical of classic Danish military architecture of the period.
Fort Frederik was the focal point of two important events that led to the dissolution of the slave-based economy of the Virgin Islands. In 1848, Emancipation Revolt ended slavery in the Danish West Indies, but inaugurated a 30-year period of serfdom based on contract labor that ensured continuing control by plantation owners. Then in 1878, escalating tensions erupted into the Labor Riot and Fireburn, which ended the contract labor system.
The fort has served as a jail, police station, fire station and courthouse since the purchase of the Virgin Islands by the U.S. in 1917.
It was listed as a contributing property in the Frederiksted Historic District in 1976. It was individually listed on the National Register of Historic Places in 1996. It was further declared a National Historic Landmark in 1997.
Fort Frederick has a display related to the Fredensborg, a ship that was part of the "Triangle Trade" from Europe, to Africa and ST. Croix and back to Europe. The ship sank just off coast in Denmark; the first mate saved the ship's log. At the Fort are records about the sale of the slaves which occurred in St. Croix.
In the ensuing years, Trygborg tower and the north curtain were demolished, along with the entire north and most of the east ravelins. The present one-story Gothic revival structure, with its centered three-tiered tower, was built between the northeast and northwest bastions to replace the demolished north curtain.