Double apron fence

One example is the "low wire entanglement", which consists of irregularly placed stakes that have been driven into the ground with only some 15 cm (six inches) showing; the barbed wire is then wrapped and tightened on to these. An enemy combatant running through the barrier, which is hard to see, is apt to trip and get caught.

Wire obstacles may have originated with Union General Ambrose Burnside during the American Civil War Battle of Fort Sanders in the Knoxville Campaign when telegraph wire was strung between tree stumps 30 to 80 yards in front of one part of the Union line. They first saw significant military use during the Second Boer War, and reached their pinnacle during World War I, Wire obstacles, together with machine guns, were responsible for many casualties in the trench warfare of World War I. 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.

Relatively elaborate obstacles were also used in some phases of the Korean War, and continue to be used on the Korean Demilitarized Zone, and a few other borders. However the more fluid nature of modern war means that most obstacles used today are relatively simple, temporary barriers.

Tanks and light armored vehicles can generally flatten unmined wire obstacles, although the wire can become entangled in the tracks and immobilize the vehicle. This can also occur to wheeled vehicles once the wire becomes wrapped around the axle. Wire obstacles can also be breached by intense artillery shelling or Bangalore torpedoes.

<gallery> Image:Knife rest.jpg|The "knife rest" or "Spanish rider" is a modern wire obstacle functionally similar to the cheval de frise, and sometimes called that. Image:Concertina wire.png|Triple concertina wire fence. Image:Obstacle belt.jpg|A complex obstacle belt of low wire entanglement backed by a double apron fence. Both obstacles have movable openings that can be blocked with knife rests. </gallery>

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