_The Terebra._--A machine based upon the classical _terebra_ was also in use. It consisted of a heavy beam which could be rotated; the iron head being furnished with a spike of square section was inserted in a joint into which it bored its way, breaking up the surrounding stones and facilitating their removal. _The Cat, or Sow_, was in constant use for mining and underpinning walls. It was a covered house upon wheels, with an enormously strong roof calculated to withstand the heavy stones, beams of wood, hot water, molten lead, and spiked poles which were invariably launched from the battlements for its destruction. Under its cover the besiegers tunnelled beneath the walls, which they supported with woodwork until their task was completed; by starting a conflagration in the chamber thus excavated the supports were consumed and the wall was breached. At other times the stones, previously shattered or loosened by the ram or the terebra, were removed until the wall above was incapable of bearing its own weight. Mining, like other operations, had to be carried out with discretion and was undoubtedly a precarious operation. Thus in the siege of Dryslwyn Castle, Carmarthenshire, in the time of Edward I., Lord Stafford and other leaders lost their lives by a sudden collapse of the walls they were undermining. The mine was often met by a counter-mine of the garrison as in modern warfare. _The Beffroi, Belfry, or Movable Tower_ was a machine for facilitating the capture of fortified positions. It could be built upon the spot or carried from place to place in pieces. When mounted upon wheels it was pushed forward towards the walls, the object being to give the assailants the same advantage of height which was shared by the besieged. From the upper platform the archers could command the battlements and approaches; those in lower stages sent their missiles into loopholes and other openings; in the lowest stage a ram was often mounted. One feature of its construction was a hinged platform which fell outwards upon the battlements and over which the assailants endeavoured to enter the fortress. The besieged hindered the approach of this terror by digging pitfalls for the wheels, shooting incendiary missiles, making sallies for its destruction by fire, or concentrating such a body of men upon the walls that none could live under the hail of missiles poured into it.