Wire entanglement
A wire entanglement was one of the most elaborate types of military wire obstacles. The entanglement could in some places be scores of metres thick and several metres deep, with the entire space filled with a random, tangled mass of barbed wire. Entanglements were often not created deliberately, but by pushing together the mess of wire formed when conventional barbed wire fences had been damaged by artillery shells.
Wire entaglements, together with machine guns, were responsible for many casualties in the trench warfare of World War I. True entanglements have rarely been seen after the end of that war, largely due to the infrequent use of trench warfare.