The Czech hedgehog (Czech: rozsocháč or ježek) is a static anti-tank obstacle defense made of metal angle or I-beams (that is, lengths with an L- or H- shaped cross section.) The hedgehog is very effective in keeping tanks from getting through a line of defense. It maintains its function even when tipped over by a nearby explosion. Although it may provide some scant cover for infantry, infantry forces are generally much less effective against fortified defensive positions than mechanized units.
The Czech hedgehog's name refers to its origin in Czechoslovakia. The hedgehogs were originally used on the Czech-German border by the Czechoslovak border fortifications - a massive but never-completed fortification system that was turned over to Germany in 1938 after the occupation of the Sudetenland as a consequence of the Munich Agreement.
The Czech hedgehog was widely used during World War II by the Soviet Union in anti-tank defense. They were produced from any sturdy piece of metal and sometimes even wood, including railroad ties. Czech hedgehogs were especially effective in urban combat, where a single hedgehog could block an entire street. Czech hedgehogs thus became a symbol of "defense at all cost" in the Soviet Union; hence the memorial to Moscow defenders, built alongside M-10 in 1966, is composed of three giant Czech hedgehogs.
A Czech hedgehog made to specifications could be constructed from any material capable of withstanding at least 60 tonnes-force (600 kN), while being at most 1.4 metres (4 ft 7 in) high. However, such parameters were hard to achieve in makeshift hedgehogs, reducing their usefulness.
The hedgehog is not supposed to be an immovable obstacle because of its size or weight. The proper size is to be slightly larger than the clearance under the enemy tank, so that a tank that attempts to move the hedgehog would instead roll on top of the hedgehog and get stuck and possibly wreck the track of the tank. These anti tank blockers used to be very common during WW2 but are now much more rare. 
Industrially manufactured Czech hedgehogs were made of three pieces of metal angle (L 140/140/13 mm, length 1.8 metres (5 ft 11 in), weight 198 kilograms (437 lb); later versions: length 2.1 metres (6 ft 11 in), weight 240 kilograms (530 lb)) joined by gusset plates, rivets and bolts (or, later in the war, welded together) into a characteristic spatial three-armed cross with each bar at right angles to the other two. (This pattern forms the axes of an octahedron.) Two arms of the hedgehog were connected in the factory, while the third arm was connected on-site by M20 bolts. The arms were equipped with square "feet" to prevent sinking into the ground, as well as notches for attaching barbed wire.
During the Normandy Invasion the Allies cut up sizable numbers of intact and wrecked hedgehogs, and welded them to the front of their M4 Sherman tanks and M5 Stuart tanks. Known as Rhino tanks, they proved very useful for clearing the hedgerows that made up the bocages across Normandy.
- Cheval de frise, a portable frame covered with many long iron or wooden spikes used in medieval times to deter cavalry.
- Dragon's teeth (fortification)
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- J A Hampton (1944). "A 23992: Royal Navy Commandos at La Riviere preparing to demolish beach obstacles (photograph)". Imperial War Museum Collection Search. Imperial War Museum. Retrieved 2 August 2012.