The construction of the Fort Regent fortress we see today began on 7 November 1806, during the Napoleonic Wars, with the laying of a foundation stone by George Don the Lieutenant Governor of Jersey. The fort was built using local workers and men from the Royal Engineers, with an average of 800 men working at any given time. This enabled the substantial amount of work to be completed 8 years later, in 1814. It was given the name Fort Regent in honour of Prince Regent, who was King of the United Kingdom of Great Britain and Ireland at this time. The design of the fort is credited to Lieutenant-General John Humfrey, and it is thought that Lieutenant-Colonel John Evelegh would have also worked on the final plans. The fort's main features are substantial curtain walls, ditches, a glacis, redoubts, bastions, and redans (or demi-bastions). There was a parade ground in the centre, which is now built upon, and covered with a roof.
During the Occupation of the Channel Islands the German forces made some additions to the fort including flak cannons. Some of these concrete structures remain today. In December 1967 the States of Jersey made a decision to adapt the site into a leisure centre.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.