Caltrop

A caltrop (also known as caltrap, galtrop, cheval trap, galthrap, galtrap, calthrop, crow's foot) is an antipersonnel weapon made up of two or more sharp nails or spines arranged in such a manner that one of them always points upward from a stable base (for example, a tetrahedron). Caltrops served to slow down the advance of horses, war elephants, and human troops. They were said to be particularly effective against the soft feet of camels. In more modern times, caltrops are used against wheeled vehicles with pneumatic tires.

The modern name "caltrop" is derived from the Latin calcitrapa (foot-trap). The synonymous Latin word tribulus gave rise to the modern Latin name of a plant offering similar hazards to sandaled or bare feet, Tribulus terrestris (Zygophyllaceae), whose spiked seed case can also injure feet and puncture tires. This plant can also be compared to the starthistle, Centaurea calcitrapa, which is sometimes called the "caltrop". A water plant with similarly-shaped spiked seeds is called the "water caltrop", Trapa natans.