Fortified points, as well as cavalry, take on additional importance when the resources of one’s opponent seldom permit him to sit down before them and maintain a blockade and regular siege for a long time. A great deal of nonsense has been talked about the “impregnability” of fortification before the discovery of gunpowder. Any man acquainted with military things knows that, even irrespective of blockade, any fortress must fall before besiegers in sufficient numbers and possessed of armament and engineering skill equal to the defenders, unless the defence can receive relief from outside. Thus Philip Augustus took Chateau Gaillard, the strongest fortress of its time, not by blockade but by regular siege. On the other hand, it has been truly observed that mediæval commanders of Philip’s type, and with his resources, were rare. The value of fortification is that it gains time, and few men of the Middle Ages had their troops well enough in hand to hold them long at the monotonous drudgery of siege work—even if they had resources sufficient to keep their force continuously in being at all. The well-provisioned fortress could usually count on starving out its besiegers before being starved out itself. Accordingly, if one party to a quarrel felt himself to be weaker than his enemy, he was apt to shut himself up promptly behind walls. Furthermore, fortifications played a large part in mediæval warfare because a fortress covering only a small area could resist a regular siege as well as one of great extent. The importance of comparatively small fortified points, that is of castles, sprang from the lack of missile weapons capable of battering down stone walls. Obviously, as the power, accuracy, and effective range of missile weapons increase, the circumference of the first-class fortress must correspondingly increase if it is to escape being overwhelmed by the converging fire of the greater number of engines which the concentric position of the besiegers enables them to bring to bear upon it. Conversely, when the problem (as in the Middle Ages) is of close-in defence only, the area to be defended matters little with reference to the siege work involved. Whereas, on the other hand, the expense of construction mounts as the circumference to be fortified increases. The resources of the besiegers were sapping or battering the base of the walls; or escalade from behind the cover of movable towers which could be set up out of range, and then rolled up so as to let down drawbridges on a level with the battlements.