That the men of the later Stone Age had developed a considerable degree of culture is proved by such remains as these. The erection of these giant chambers must have called for a vast amount of co-operation, skill, and ingenuity. The means whereby the massive stones were placed into position, and so fixed to withstand the shocks of thousands of years, have not yet been satisfactorily explained by archæology. ] The stone blocks of which these gigantic structures are piled now often lie bare. Large stones placed crosswise, which represent, as it were, the side-walls of a room, support a roof of one or several “covering-stones” of occasionally colossal size. For the erection of these in their present position without the technical resources at the disposal of modern builders, human strength appears inadequate; in popular opinion only giants could have made such structures. Some of the stones are really so large, and the covering-stones especially so enormous, that these buildings have defied destruction, for thousands of years, by their very weight. In the time of their construction these giants’ graves were mostly buried under mounds. They were the inner structures of large tumuli, in which the reverence of the men of the Stone Age once buried its heroes. One of the finest “giant’s chambers” is probably that near Öm, in the neighbourhood of Roskilde, in Denmark. The building material consists merely of erratic stone blocks of enormous size. The rough blocks were mostly set up by the side of one another, without any further working, so as to support one another as far as possible; at the same time all of them, as Sophus Müller observes, are slightly inclined inward, so that they are kept more firmly in position by their own weight. The stones thus erected, forming the parallel side-walls of the whole structure, stand so far apart that a huge erratic block, reaching from one wall to the other, could be placed on them as a roof. The distance between the side-walls of the giant’s chambers attains a maximum of eight to nine feet; the covering-stones placed on them are some ten to eleven feet long. The pressure of the covering-stones from above helps considerably to hold the whole structure together. In order to distribute the pressure of the covering-stones regularly, smaller stones were carefully inserted under the wall-stones where they had to stand on the ground. How exactly these proportions of weight were judged is proved by the fact that these structures of heavy and irregular stones, resting on their natural, differently shaped sides and edges, have held together until the present day. The inner walls of the chambers were made as carefully as possible. Where, as on the outside, the rough and irregular form of the stone block projects, either the naturally smooth side was turned inward or the roughness was chipped off. [Illustration: THE MARVELLOUS MEMORIALS OF THE STONE AGE AT CARNAC IN BRITTANY