An hypothetical castle in a forest near Saragossa. It represents that terrible obstacle which fear conjures up, but which vanishes into thin air as it is approached by a stout heart and clear conscience. The allegory forms the third part of the legend of Croquemitaine.
“If a child disappeared, or any cattle were carried off, the trembling peasants said, `The lord of Fear-fortress has taken them.' If a fire broke out anywhere, it was the lord of Fear-fortress who must have lit it. The origin of all accidents, mishaps, and disasters was traced to the mysterious owner of this invisible castle.”— Croquemitaine, iii. 1.
It sunk before my earnest face, It vanished quite away, And left no shadow on the place, Between me and the day. Such castles rise to strike us dumb; But, weak in every part, They melt before the strong man's eyes And fly the true of heart.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894