Little requires to be said of the tombs of the Persians; that of Darius is represented in plan and elevation in Woodcut No. 92, and, as before remarked, it is a literal copy on the rock of the façade of his palace. Internally, three small cells contained the remains of the king, with those of the persons, probably his favourite wife or wives for whom he had destined that honour. Close by this, at Naksh-i-Rustam, are four others, and in the rock behind Persepolis are three more tombs of the Achæmenian kings, identical with these in all essential respects; but still with such a difference in workmanship and detail as would enable a careful architectural student easily to detect a sequence, and so affix to each, approximately at least, the name of the king whose sepulchre it is. Unfortunately, that of Darius only is inscribed; but his position in the dynasty is so well known, that, starting from that point, it would be easy to assign each of these tombs to the king who excavated it for his own resting-place. Although these tombs of the Achæmenians are not remarkable for their magnificence, they are interesting in an architectural point of view, inasmuch as—as pointed out above—they enable us to restore their structural buildings in a manner we would hardly be able to do without their assistance. They are also interesting ethnographically as indicating that these kings of Persia were far from being the pure Aryans the language of their inscriptions would lead us to suspect they might be. There are not, so far as is yet known, any series of rock-cut sepulchres belonging to any dynasty of pure Aryan blood. Nor would any king of Semitic race attempt anything of the sort. Their evidence, therefore, as far as it goes—and it is tolerably distinct—seems to prove that the Achæmenian kings were of Turanian race. They only, and not any of their subjects in Persia, seem to have adopted this style of grandeur, which, as we shall presently see, was common in Asia Minor, and other countries subject to their sway, but who were of a different race altogether. CHAPTER V. INVENTION OF THE ARCH. Before leaving this early section of architecture, it may be as well briefly to refer to the invention of the true arch, regarding which considerable misconception still exists. It is generally supposed that the Egyptians were ignorant of the true principles of the arch, and only employed two stones meeting one another at a certain angle in the centre when they wished to cover a larger space than could conveniently be done by a single block. This, however, seems to be a mistake, as many of the tombs and chambers around the pyramids and the temples at Thebes are roofed by stone and brick arches of a semicircular form, and perfect in every respect as far as the principles of the arch are concerned.