In World War I, no man's land often ranged from several hundred yards to in some cases less than 10 yards. Heavily defended by machine guns, mortars, artillery, and riflemen on both sides, it was often extensively cratered, and was riddled with barbed wire, rudimentary improvised land mines, as well as corpses and wounded soldiers who were unable to make it through the hail of bullets, explosions, and flames. The area was sometimes contaminated by chemical weapons. It was open to fire from the opposing trenches and hard going generally slowed any attempted advance.