The Royal Commission on the Defence of the United Kingdom, which Lord Palmerston had established in 1859 in response to a perceived threat of invasion by Emperor Napoleon III of France, recommended the fort's construction in Tenby. The design of the fort is credited to Colonel William Jervois. It is a simple rectangular work, consisting of three artillery casemates on two opposite sides, for RML 7-inch guns firing through iron shields. A further three gun platforms for RML 9 inch 12 ton guns are located on the roof. The guns facing north were intended to cover Tenby Harbour and the beach towards Saundersfoot, while those facing south covered the beach towards Penally. The entrance at the western (landward) end of the fort is approached by means of a drawbridge over a dry ditch and is defended by two caponiers or 'flanking galleries', each of three storeys pierced with loopholes for small arms fire. At the eastern end at basement level are located the powder magazine and shell store. There was accommodation for a garrison of 150 men.
The work was completed by 1870. In 1907 the fort was decommissioned and sold to the Windsor Richards family who converted it into a private house. The gun shields were replaced by windows and the interior was lavishly decorated, although the fort was apparently garrisoned by the army during the First World War. During the Second World War, the fort was compulsory purchased in 1940 and the house contents were auctioned by Harrods. During the war an anti-aircraft battery was built in front of the fort; units serving there included the Royal Marines, 4th Defence Battery and a Light Anti-Aircraft Battery of the Royal Artillery, a detachment of the Belgian Army, the Home Guard, and an Air Sea Rescue detachment of the RAF.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.