caltrop

A metal object, usually small, with spikes arranged so that, when thrown onto the ground, one always faces up as a threat to pedestrians, horses, and vehicles (also used as a heraldic charge).

[…] her father, the emperor Alexius, who reigned AD 1081-1118, ordered caltrops to be cast in front of his archers […]

By Sung times, several different types of caltrops had been developed. As in earlier times, both caltrops could be made from both wood and iron...

The starthistle, Centaurea calcitrapa, a plant with sharp thorns.

Any of a number of flowering plants in the family Zygophyllaceae, including several members of the genus Kallstroemia and the species Tribulus terrestris, native to warm temperate and tropical regions.