These military tunnels were formed by hollowing out the rock on which the city of Luxembourg was built. They date back to 1644, the time when Luxembourg was under Spanish rule. The French military engineer Vauban enlarged the Petrusse casements when he captured the city 40 years later. The honeycomb of tunnels, including the Bock Casements, run for 15 miles below the city. They contained barracks, bakeries, slaughterhouses and a well. The fortifications were dismantled after the Treaty of London, but since 1933 the public have been able to view some of the tunnels.