Governor Jørgen Iversen led the second expeditionary force from Denmark to St. Thomas, where he arrived on May 25, 1672; there, he initiated construction of Fort Christian, named after Danish King Christian V. By 1676, builders had completed the fort's outer walls and placed a three-story oval tower in the courtyard against the north curtain. Trygborg, as the tower was named, had gun platforms on its two upper stories and roof. In February 1678, two years after construction began, a French force attacked St. Thomas and was repulsed.
Until it was demilitarized during the 1870s, the fort underwent enlargement and repair; after the military departed, Fort Christian served as the police headquarters of the Virgin Islands. 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.