Caltrop

A caltrop (also known as caltrap, galtrop, cheval trap, galthrap, galtrap, calthrop, jackrock or 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 were part of defenses that served to slow the advance of horses, war elephants, and human troops. They were particularly effective against the soft feet of camels. In more modern times, caltrops are still effective when used against wheeled vehicles with pneumatic tires.

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

According to Quintus Curtius (IV.13.36), iron caltrops were used as early as 331 BC by Darius III against Alexander the Great at the Battle of Gaugamela in Persia.

They were known to the Romans as tribulus or sometimes as murex ferreus, the latter meaning 'jagged iron' (literally 'iron jagged thing'). They were also used in the Battle of Carrhae in 53 BC.

The late Roman writer Vegetius, referring in his work De Re Militari to scythed chariots, wrote:

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