470 Primitive Greece : Mycenian Art. surface : the arrangement of the polygons, which form a net-like structure, with uneven and dissimilar meshes, is intentional. The fineness of joint shown here is unknown to the two first systems, where there always remains some cavity which has to be made good with clay or pebbles. In polygonal construc- tion, on the contrary, each block is cut in shape so as to fit it exactly to the contiguous stones, the concave angles of the one adjusting themselves with the utmost nicety to the saliences of the adjoining units. This implies a skilful and trained hand in cutting the blocks, for which they apparently used a shifting-bevel (Fig. 183).^ Polygonal masonry appears on the main and small sides of the Mycenian bastion, and as facing to the south-western tower (Fig. 90, and PI. IX.), where each joint is perfect. On this well-arranged mass time has had no more hold than would Fig. 183. — Polyconal stones and shifting bevel. a hostile force in by-gone days, had an attempt been made to effect an assault on this side. The vertical height of this wall is still ten metres ; it makes a rare brave show, and compares favourably with the mutilated condition of the Cyclopaean pieces adjoining it. Polygonal work only appears on three points of the enclosure, and always alongside or above the two other systems, never below them : whence we may safely infer that its presence corresponds with later rebuildings ; here it may have been necessary to rectify the trace of the wall, there to close a breach made by the enemy. Steffen is inclined to think that the section of the rampart enclosing the sepulchres on the acropolis dates from the time when the royal cemetery became a species of sanctuary sacred to the memory of glorious ancestors ; the direction of the wall ^ Aristotle may have some such instrument in view when he speaks of " the leaden and elastic rule of the Lesbian mason, which adapts itself to the stone."
