5. The dominion of the Kaliphs down to its destruction in 1258 A.D. 6. The last period continuing to our own time. The mythic and historical periods of Persia resemble two diverging lines, of which the undoubted fact of the reign of Kai-Khorus forms the connecting point. Whilst the historical line grows more and more distinct as it proceeds, the mythic line retreats farther and farther into the dim region of the unknown. Passing from the known to the unknown, we must assign to the development of Zend thoughts, institutions, mode of writing, and mode of building, a greater antiquity than to the Assyrian and Babylonian monuments. Of Persian remains we possess nothing but skeleton buildings, which, from the entire absence of connecting walls, lead us to infer that they were still mere tents, and that the textile fabric had not yet undergone the further process of incrustation in stucco or stone sculpture. This is not the case with Nineveh and Babylon, the great towns, or, as we should say, the great empires, on the Tigris and Euphrates. Through the indefatigable exertions of the Right Hon. Mr. Layard, M. Botta, Lord Loftus, and Mr. Rassam, we possess now, in London and Paris, tablets with records more than 3,000 years old. The boundary stones prove that some fixed laws regulated territorial property, even at these remote periods. The personal ornaments, consisting of mother-of-pearl studs, silver rings, bracelets, gold and pearl earrings, beads, and shell-bosses with bronze pins, testify to a high civilisation. The mode of writing in Nineveh and Babylon was borrowed from the Zend people; and the religious conceptions of the Persians are undoubtedly older than the already-complicated idolatry based on the astronomical notions of the Assyrians and Babylonians. The Zend-Avesta (meaning the living word) may be said to be like an Egyptian Nile-meter, erected on the primeval soil of history, measuring the yearly deposits and alluvial sediments of by-gone ages. Through the pure crystals of myth and poetry we may see the inner formation of society, whilst from without the vast construction of history is mysteriously going on. We wander through endless lines of Memnon statues, all resounding with the legends of past ages, in perusing the Zend-Avesta, and are suddenly led before the fountain of all matter, at which the high-priest stands, commanding in the harmony of the seven planets the birth of the world, and the origin of all things.