Area denial weapon

Caltrops
Area denial weapon - Wikipedia - http://en.wikipedia.org/wiki/Area_denial_weapon

Area Denial Weapons: Caltrops, Punji Sticks, Spring-Guns and More | Prepare. Think. Survive - http://preparethinksurvive.com/caltrops/

Caltrop
http://upload.wikimedia.org/wikipedia/commons/thumb/5/59/Caltrop_from_Vietnam_1968.jpg/510px-Caltrop_from_Vietnam_1968.jpg