There seems to be no doubt that the outer stone circle originally consisted of thirty square piers, spaced tolerably equally in the circle. Though only twenty-six can now be identified, either standing or lying in fragments on the ground, it seems equally certain that they were all connected by a continuous stone impost or architrave, though only six of these are now in _situ_.[111] The diameter of the circle is generally stated to be about 100 feet, and as this has been suggested as a reason for its being considered as post-Roman, it is important to know what its exact dimensions are. It turns out that from the face of one pier to that of the opposite one, where both are perpendicular, the distance is 97·6, or exactly 100 Roman feet. The distance from the outer face of these piers to inside of the earthen vallum that surrounds the whole is again 100 feet, though that cannot now be ascertained within a foot or two, or even more; but as this makes up the 100 yards and the 100 feet which recur so often in these monuments, these dimensions can hardly be considered accidental, and "valeant quantum" are an indication of their post-Roman date.[112] Inside these outer circles stand the five great trilithons. Since the publication of Sir R. Colt Hoare's plan, their position and plan may be considered as settled. According to him, the height of the outer pair is 16·3, of the intermediate pair 17·2, and of the great central trilithon as it now stands 21·6. In their simple grandeur they are perhaps the most effective example of megalithic art that ever was executed by man. The Egyptians and Romans raised larger stones, but they destroyed their grandeur by ornament, or by their accompaniments; but these simple square masses on Salisbury plain are still unrivalled for magnificence in their own peculiar style. All the stones in these two great groups are Sarsens, as they are locally called, a peculiar class of silicious sandstone that is found as a local deposit in the bottoms of the valleys between Salisbury and Swindon. It is the same stone as is used at Avebury, the difference being that there the stones are used rough in their natural state, here they are hewn and fitted with very considerable nicety. Each of the uprights has a tenon on its surface, and the undersides of the architrave, or horizontal piece, have each a mortice, or rather two mortices, into which these tenons fit with considerable exactness. [Illustration: 23. Stonehenge as at present existing, from Mr. Hawkshaw's plan.]