Strategic Topography
Luxembourg's urban core is structured by the Alzette and Pétrusse river canyons. The city functioned as a primary European fortress between the 10th century and 1867. The "Gibraltar of the North" designation refers to the 17km of subterranean casemates and multiple defensive rings.
The 1867 Treaty of London resulted in the dismantling of the fortress walls, leaving only 10% of the original masonry. This heritage is now managed under UNESCO World Heritage standards, balancing medieval ruins with the modern administrative functions of the Grand Duchy.