The slingers and archers were aided in their death-dealing business by the workers of the catapults, machines which, framed somewhat upon the principle of the medieval crossbow, discharged gigantic javelins and beams headed with iron. The Jews did not remain passive under this attack. In the use of the bow and the sling they were almost as well skilled as their opponents, and returned the fire of the besiegers with a fire equally brisk. The fray became more deadly as soon as the Romans had got their balistæ into action. These were huge machines, whose working part consisted of an arrangement of levers and ropes, which, when forcibly drawn back and let go, produced a tremendous recoil, sufficient to hurl ponderous stones to a distance of three furlongs, and farther. These stones were discharged mainly for the purpose of carrying away the battlements, turrets and parapet of the wall, so that, deprived of cover, the defenders would be compelled to quit the ramparts, since to remain there open and exposed would mean certain death at the hands of the archers and slingers. The withdrawal of the defenders would be the signal for the escalade. More than fifty of these balistæ were now at work, making terrible havoc, not only with battlement and parapet, but also with the lives of the Jewish people. Some of the stones hurled aloft exceeded three hundred pounds in weight, and had force sufficient to kill six men, if taken in file. Josephus describes how he saw a man’s head struck clean from his shoulders and carried to a distance of three furlongs! Anyone standing within a yard of such stone as it swept past was certain to be flung to earth by the accompanying rush of air. Such was the effect of the ponderous rocks that now went whirling over the ramparts, fifteen or twenty at a time, into the suburb of Bezetha, crashing through the roof and wall of many a private dwelling, and tumbling it into ruins amid the wild shrieking of its hapless occupants. To this artillery Simon sought to reply with the captured Roman balistæ; but the Zealots, for lack of skill and practice, bungled so miserably at the task as to evoke the laughter of the enemy. While this terrific fusillade was going on, a party of Romans began to push forward a pluteus--a sort of iron shed open at both ends and running upon wheels. As it moved along, the Romans walked beneath its roof, and were thus effectually screened against the missiles showered at them from the battlements. As soon as the pluteus touched the foot of the wall, the party within, kneeling down upon the ground, set to work vigorously with lever and crow, endeavoring to loosen the lower courses of the masonry.