They are historically a development of the Caltrop, with anti-cavalry and anti-personnel versions being used as early as 331 BC by Darius III against Alexander the Great at the Battle of Gaugamela in Persia. During WW1 there set up booby traps on small roads or mountain tracks by soldiers or thrown from an airplane. They have the characteristic of having four points so that even when thrown in the air there is always the point upwards ready to hurt a soldier or a horse or a mule. This group of three measure approximately 14cm across. No markings. Heavy oxidation. Most probably Italian WW1.