I have made this division into three periods merely to point out the different architecture of the walls, and with no intention of maintaining that the one must be more ancient than the other. On the contrary, after mature consideration, I cannot think that the one kind of wall should be considered older than the other, for, after the circuit walls had once been built of rough stones of enormous size, it is hardly possible that in after times part of them should have been destroyed in order to replace them by walls of another type. Or if part of the primitive walls had been razed by an enemy, there could have been no reason why they should not be restored in the same style, which was quite as solid as the other, and was besides much cheaper and easier, because only the wall could have been destroyed, but not the stones, which lay ready to be put up again. It appears also to have been the custom of the primitive builders to pay a little more attention to symmetry and regularity in the more monumental portions of their work. I conclude, therefore, that the three kinds of architecture existed simultaneously in that remote age of antiquity when the walls of Mycenæ were built, but that in later times the style of architecture marked as of the "first period" went out of fashion, and the two other modes of building alone remained in use. Walls of polygonal blocks continued in use in Greece until the time of the Macedonian dominion; a proof of which is seen, for instance, in the masonry of the sepulchres at the Hagia Trias in Athens, as well as the fortifications on the island of Salamis, of which we know with certainty that they were erected in the fourth or fifth century, B.C.[107] Within the last sixteen years walls of polygonal blocks have come extensively into use in Sweden and Norway, particularly for the substructions of railway bridges. The first western terrace is bordered on its east side, for a distance of 166 feet, by a Cyclopean wall 30 feet high, which is crowned by the ruins of a tower, and runs parallel with the great circuit wall; it is no doubt part of a second enclosure.[108] Remnants of other enclosures are visible a little higher up the mount to the left, as well as on the eastern side. A second interior tower appears to have stood at the south-western corner of the summit. Near the north-western corner the circuit wall is traversed by an ogive-like passage 16½ feet long, like those of Tiryns (see No. 20). Traces of Cyclopean house-walls and foundations can be seen on all but the first eastern and western terraces. [Illustration: No. 20. Entrance to the ogive-like Gallery in the Walls of the Citadel of Mycenæ.]