Many conjectures have been made as to how the huge capstones of the circle at Stonehenge were placed on the erect stones. Sir Henry Dryden thought that when the upright stones were set on end, earth or small stones were piled around them until a large inclined plane was formed, on which "skids" or sliding-pieces were placed. Then the caps were placed on rollers, and hauled up by gangs of men. Probably in some such way these wonderful monuments were formed.
The last class of rude stone monuments is composed of dolmens, or chambered tombs, so named from the Welsh word _dol_, a table, and _maen_ or _men_, a stone. They are in fact stone tables. Antiquaries of former days, and the unlearned folk of to-day, call them "Druids' altars," and say that sacrifices were offered upon them. The typical form is a structure of four or more large upright stones, supporting a large flat stone, as a roof. Sometimes they are covered with earth or stones, sometimes entirely uncovered. Some antiquaries maintain that they were always uncovered, as we see them now; others assert that they have been stripped by the action of wind and rain, and snow, frost, and thaw, until all the earth placed around them has been removed. Possibly fashions changed then as now; and it may console some of us that there was no uniformity of ritual even in prehistoric Britain. Dolmens contain no bronze or iron implements, or carvings of the same, and evidently belong to the time of the Neolithic folk.
Among prehistoric remains none are more striking than the great camps and earthworks, which hold commanding positions on our hills and downs, and have survived during the countless years which have elapsed since their construction. Caesar's camps abound throughout England; it is needless to say that they had nothing to do with Caesar, but were made long years before the Conqueror ever set foot on British land. These early camps are usually circular in shape, or follow the natural curve of the hill on which they stand. Roman camps are nearly always square or rectangular. They consist of a high vallum, or rampart of earth, surrounded by a deep ditch, and on the _counterscarp_, or outside edge of the ditch, there is often another bank or rampart. The entrance to these strongholds was often ingeniously contrived, in order that an enemy endeavouring to attack the fortress might be effectually resisted.