What Is: a Caltrop

One of the more dreaded events on a Medieval battlefield was a charge of knights or mounted men-at-arms, riding down foot soldiers who had little or no place to flee.  There were various measures taken to ward off horses on a battlefield, from pike formations such as the schiltron to a nasty little antipersonnel device known variously as a caltrop, cheval trap, jack-rook or crow's foot.  These devices were made of two or more spikes arranged in a formation so that, when thrown on the ground, one of the spikes always points upward.  A horse running over these weapons would get them embedded in the soft part of the foot and go down, taking its rider with it.  A pile of downed horses and riders created fearful mayhem on any battlefield.

The name caltrop comes from a French corruption of the Latin words for a foot-trap, which is exactly what it was intended.  They were first used by Roman armies in dealing with horses or even war elephants, who were just as susceptible to the spikes.  Medieval armies used them, including Scottish armies facing English knights during the battles of Wallace and Bruce, and they remained in use during the early modern era.  Settlers in Jamestown, Virginia kept a supply of them on hand for use against Native warriors who sometimes fought barefoot.  They were also used during World War I, where Australian troops knew them as horse chestnuts.  Representations of a caltrop are used as military insignia by units who trace their heritage to horse cavalry, such as the U.S. Army's 3rd Corps, at Fort Hood, Texas.