What is Czech hedgehog?

The Czech hedgehog is a static anti-tank obstacle defense made of metal angle beams or I-beams. The hedgehog is very effective in keeping light to medium tanks and vehicles from penetrating a line of defense; it maintains its function even when tipped over by a nearby explosion. Although Czech hedgehogs may provide some scant cover for attacking infantry, infantry forces are generally much less effective against fortified defensive positions than mechanized units.