German Panzer divisions circumvented the massive fortifications by advancing through the Ardennes forest, an area French commanders mistakenly believed was impassable.

The phrase has become a common metaphor for any expensive, elaborate strategy that creates a false sense of security while leaving its creators vulnerable to new tactics.

To keep soldiers comfortable underground for long deployments, the massive subterranean forts included recreation areas, wine cellars, and advanced ventilation systems.

Extending the wall along the border would have forced France to abandon its strategy of fighting in Belgium, effectively leaving the neutral nation defenseless.