Chevaux-de-frise is a military obstacle that consists of a series of wooden or metal spikes or bars that are driven or placed into the ground to prevent the enemy from advancing. Some synonyms for chevaux-de-frise include abatis, cactus, hedgehog, and palisade. Abatis refers to a defensive barrier formed by felled trees with their branches pointing outwards. Cactus is a prickly plant that can be used to create a similar impediment. Hedgehog is a term used to describe objects or devices with spikes or protrusions that serve to deter or impede attackers, while palisade is a fence made of wooden stakes or other materials.