Underground secrets of Luxembourg

Luxembourg, among others, has a deep military tradition and may boast its knowledge on how to protect the city from unwelcome visitors.  There are two casemates underneath the Luxembourg city. Nowadays they are two separate places. However, only two centuries ago it was one common net of underground corridors and connections.

I had been living in Luxembourg for three years and had never visited the casemates, the top tourist attraction of the city. One August Sunday we decided to correct this mistake and headed to the Bock Casemate.

The Bock (Luxembourgish: Bockfiels) is the old historical district in the north-eastern corner of Luxembourg City. The rocky cliffs tower above the River Alzette surrounds the city on three sides and offer a natural fortification. The first artificial fortification was built by the Count Siegfried in 963. It was a castle, which became a basis for the development of the town lately called Luxembourg. Over the centuries, the Bock and the surrounding defences were reinforced, attacked and rebuilt again as the armies of the Burgundians, Habsburgs, Spaniards, Prussians and French vied for victory over one of Europe’s most strategic strongholds.

Fights for the strategic point in the heart of Europe did not stop until the Treaty of London was signed in 1867. As a condition of the Treaty, the fortifications had to be desolated. Nowadays ruins of the old castle and the underground system of passages and galleries continue to be a major tourist attraction.

Over the centuries, Siegfried’s fortified castle on the Bock was considerably enlarged and protected with additional walls and defences. In 987, the castle chapel was built at the nearby Fish Market which is nowadays replaced by the St. Michel’s church. UnderConrad I, the castle became the residence of the Counts of Luxembourg. The town was attached numerous amount of times and each time a new owner rebuilt and fortified the castle and the casemates.

As time passed, the fortifications needed to be adapted to new methods of war based on increasingly strong firepower. During the 1640s under the Spaniards, the Swiss engineer Isaac von Treybach significantly reworked the defences. The Bock was also strengthened with three forts, the Large Bock, Middle Bock and Small Bock (from west to east), separated from each other by cuts in the rock and linked by bridges. As a result, little remained of the medieval castle.

A little later in 1684, on behalf of Louis XIV, Vauban succeeded in capturing the city of Luxembourg during a month-long siege under which the Bock fortifications were completely flattened. Thereafter Vauban, perhaps the most competent fortification engineer of his day, undertook major additions to the defences, realizing that underground passages and chambers were just as important as the surface installations. The Large Bock, connected to the old town by the Pont du Château, was further reinforced. Enclosed by a wall 12 m (39 ft) high, it was the major component of the new fortress.

In addition to these structures, the Bock also included a system of casemates which originated in the cellars of the medieval castle. In 1744, during the Austrian period, these underground passages were considerably enlarged by General Neipperg. The main passage. which still remains, is 110 m long and up to 7 m wide. Branches leading off on either side were equipped with no less than 25 cannon slots, 12 to the north and 13 to the south, offering considerable firepower. In the event of war, the Bock casemates, covering an area of 1,100 m2, could be used as barracks for several hundred soldiers. Water was supplied from a well 47 m deep.

Thanks to its defences, in 1794 during the French Revolutionary Wars, the city held out against the French siege for seven months. When the garrison finally surrendered, the walls were still unbreached. This led the French politician and engineer Lazare Carnot to call the Luxembourg fortress “the best in the world, apart from Gibraltar”. As a result, it has often been called the Gibraltar of the North.

The fortifications were finally demolished under the terms of the Treaty of London in 1867. The demolition took 16 years and cost the enormous sum of 1.5 million gold francs.

The first tunnels for the underground defences below the old castle were dug out during the Spanish period in 1644. Extensions were made by the French engineer Vauban under Louis XIV in 1684 but it was from 1737 to 1746 that the Austrians completed the extraordinary complex of underground passages and galleries known as the casemates. With a total length of 23 km (14 mi) and depths of up to 40 m (130 ft), they accommodated 50 cannons and a garrison of 1,200 men. In addition, they had underground facilities for housing equipment and horses as well as workshops, kitchens, bakeries and slaughterhouses. When the surface fortifications were dismantled in 1875, most of the underground defences remained largely untouched, 17 km (11 mi) of passageways remaining. In 1994, the casemates were added to the list of UNESCO’s world heritage sites, attracting some 100,000 visitors a year.

In 1933, the Bock casemates were opened to the public. During the Second World War, they were used as a bomb shelter able to accommodate up to 35,000 people. Renovation work and repairs were undertaken in 2008–2009 including the opening up of the mine galleries which contained explosives able to blow up part of the Bock in case of need.

Today the Bock casemates can be visited from March to October from the Rue Sigefroid.

The stairs down from the entrance lead to the huge archaeological crypt where wall plates give an overview of the history of the fortifications. More stairs lead down through the dungeons of Siegfried’s old castle to the casemates themselves, a series of long tunnels down into the rock parallel to the road above. There are a number of lateral passages as well as chambers and balconies with openings to the north and south. Once emplacements for cannons, today they offer views of the Alzette valley below.