In 963, Count Siegfried built a fortified castle on the Bock promontory, which was soon to become the cradle of the city. In the course of the centuries, on the western side, mighty ring walls were added, which, however, did not foil the Burgundians in their attempt to conquer the city in 1443. The best builder-engineers of the new masters (the Burgundians, the Spaniards, the French, the Austrians and the German Confederation) eventually turned the city into one of the most powerful emplacements in the world, the "Gibraltar of the North".

Its defences were bolstered by three fortified rings with 24 forts, 16 other strong defensive works and a unique 23 km long network of casemates: these could not only shelter thousands of soldiers and their horses, but also housed workshops, kitchens, bakeries, slaughter-houses etc. In 1867, after the declaration of neutrality,the military withdrew from the fortress and during the following 16 years 90% of the defences were demolished. In 1875, the superstructure of the Bock, a tremendous construction, was razed. However, it proved to be impossible to blow up the casemates, without also demolishing part of the city, so the entrances and the key connecting galleries were sealed. In spite of this, 17 kilometres of tunnels remain, often on different levels and tremendous stairways penetrateup to 40 metres inside the rock face. It goes without saying that these galleries functioned as shelters during the world wars, providing space for 35,000 people in case of air raids or shelling.

Small wonder that the fortifications and the historic old town enjoy world wide fame: in 1994 they were designated a UNESCO World Heritage Site.

Today 2 casemates are open to the public: the ones of the Bock promontory and those of the Petrusse Valley !!!

Opening planned: 2010 !

The transformation of "Dräi Eechelen" (Three Acorns), the nick name for Fort Thüngen, into a Museum has required major renovation work. Partially hidden underground following the demolition in 1867 and covered with abundant vegetation, the fort and its surroundings are today the subject of excavation, restoration and rebuilding work with the aim of returning them to their former glory, whilst integrating a contemporary museum space. The Museum, including the underground gallery, forms an integral part of the Vauban Circuit. The museography to come will depict an attractive combination of the fortification legacy in Luxembourg, the history of the Grand Duchy, and the different aspects of its national identity.