A caltrop (calthrop, jack rock, star nail or crow's foot) is a 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 serve to slow down the advance of horses, war elephants, and human troops. It was said to be particularly effective against the soft feet of camels. In more modern times, caltrops are used against wheeled vehicles with pneumatic tires. In Japan such devices were known as makibishi.
