At six o'clock the British guns opened a barrage, compared with which the German fire paled into insignificance. Eighteen-pounders and 4.5-inch howitzers, supported by the giant 12- and 14-inch long-range guns farther back, threw tons of metal upon the enemy lines, the heavier projectiles hurtling overhead with a roar like that of an express train. The earth trembled, and the sky was lurid with the flashes of bursting shells, as rapidly the strongly constructed pill-boxes were beaten into fragments of riven concrete.