There was also an engine called an _arbalast_, or _spurgardon_, or _espringale_, which was a huge cross-bow mounted on wheels, so as to be movable like a field-piece; it threw great pointed bolts with such force as to pass successively through several men. If the engines of the besiegers were silenced, or failed to produce any decisive impression on the place, the captain of the assailants might try the effect of the ram. We seldom, indeed, hear of its use in the Middle Ages, but one instance, at least, is recorded by Richard of Devizes, who says that Richard I., at the siege of Messina, forced in the gates of the city by the application of the battering-ram, and so won his way into the place, and captured it. The walls of mediæval fortifications were so immensely thick, that a ram would be little likely to break them. The gates, too, of a castle or fortified gate-tower were very strong. If the reader will look at the picture of a siege of a castle, given on page 373, he will see a representation of a castle-gate, which will help him to understand its defences. First he will see that the drawbridge is raised, so that the assailant has to bridge the moat before he can bring his battering-ram to bear. Suppose the yawning gulf bridged with planks or filled in with fascines, and the ram brought into position, under fire from the loops of the projecting towers of the gate as well as from the neighbouring battlements, then the bridge itself forms an outer door which must first be battered down. Behind it will be found the real outer-door, made as strong as oak timber and iron bolts can make it. That down, there is next the grated portcullis seen in two previous woodcuts, against which the ram would rattle with a great clang of iron; but the grating, with its wide spaces, and having plenty of "play" in its stone groove, would baffle the blows by the absence of a solid resistance, and withstand them by the tenacity of wrought-iron. Even if the bars were bent and torn till they afforded a passage, the assailants would find themselves in the narrow space within the gate-tower confronted by another door, and exposed to missiles poured upon them from above. It is, perhaps, no wonder that we hear little of the use of the ram in mediæval times; though it might be useful occasionally to drive in some ill-defended postern.