Inmedieval fortification, atrou de loup (French:[tʁud(ə)lu],lit. 'wolf hole'; pluraltrous de loup, also commonly referred to as atiger pit in the East) was a type ofbooby trap or defensive obstacle. Each trou de loup consisted of aconical pit about 2 m (6 ft 7 in) deep and 1.2 to 2 m (3 ft 11 in to 6 ft 7 in) wide at the top. At the bottom of the pit, a sharpenedpunji stick (wooden stake) would be hammered in.^[1] In some cases, the pit was concealed by light cover ofwicker and a layer of soil.

Trous de loup might be found singly as a trap (in which case they were always concealed), or in a dense pattern with no gaps between pits, used as an obstacle in front of a defended position.

A field of trous de loup could be made more effective if subsequently flooded to a shallow depth, which would conceal the pits, make their sides slippery, and add the risk ofdrowning.

Sometimes rotting meat or feces would be smeared onto the points to cause serious infection or death.^{[citation needed]}

Even though the term has a medieval origin, this kind of device was first described byJulius Caesar, in the seventh book of hisCommentarii de Bello Gallico (Commentaries on the Gallic Wars), who employed the device during thesiege of Alesia. Caesar writes they were calledlilies for their resemblance tothe flower of the same name.^[2] Later Roman examples can be seen atRough Castle on theAntonine Wall in Great Britain.