France constructed the Maginot Line — a vast complex of fortifications along its border with Germany — between 1930 and 1936, at enormous expense, in response to the trauma of the First World War. The line of forts, bunkers, anti-tank emplacements, and underground installations extended for hundreds of kilometres and was considered impregnable. When Germany invaded France in May 1940, they simply went around it through Belgium, rendering the entire fortification strategically useless and transforming its name into a byword for defensive futility.

The Maginot Line's spectacular failure gave poets and writers a ready-made metaphor for the futility of defensive thinking, rigid strategy, and the false security of fortification. W. H. Auden's political poetry of the 1930s and 40s drew on such images of misplaced military confidence. The phrase 'Maginot mentality' entered political discourse and poetry as a figure for any form of self-deluding defence; the castle-as-refuge had become, in the modern age, a castle-as-trap.