Still further to the west, and forming the boundary of the Empire in this direction, lay the district of the Cyrenaica, a tract of singular fertility and beauty. Between Benghazi, in east longitude 20°, and the Ras al Tynn (long. 23° 15’), there rises above the level of the adjacent regions an extensive table land, which, attracting the vapors that float over the Mediterranean, condenses them, and so abounds with springs and rills. A general freshness and greenness, with rich vegetation in places, is the consequence. Olives, figs, carobs, junipers, oleanders, cypresses, cedars, myrtles, arbutus-trees, cover the flanks of the plateau and the hollows which break its surface, while the remainder is suitable alike for the cultivation of cereals and for pasturage. Nature has also made the region a special gift in the laserpitium or silphium, which was regarded by the ancients as at once a delicacy and a plant of great medicinal power, and which added largely to the value of the country. Such was the geographical extent of the Persian Empire, and such were the chief provinces which it contained besides those previously comprised in the empires of Media or Babylon. Territorially, the great mass of the Empire lay towards the east, between long. 50° and 75°, or between the Zagros range and the Indian Desert. But its most important provinces were the western ones. East of Persepolis, the only regions of much value were the valleys of the Indus and the Oxus. Westward lay Susiana, Babylonia, Assyria, Media, Armenia, Iberia, Cappadocia, Asia Minor, Cyprus, Syria, Palestine, Egypt, the Cyrenaica--all countries of great, or at least considerable, productiveness. The two richest grain tracts of the ancient world, the best pasture regions, the districts which produced the most valuable horses, the most abundant of known gold-fields, were included within the limits of the Empire, which may be looked upon as self-sufficing, containing within it all that man in those days required, not only for his necessities, but even for his most cherished luxuries. The productiveness of the Empire was the natural result of its possessing so many and such large rivers. Six streams of the first class, having courses exceeding a thousand miles in length, helped to fertilize the lands which owned the sway of the Great King. These were the Nile, the Indus, the Euphrates, the Jaxartes, the Oxus, and the Tigris. Two of the six have been already described in these volumes, and therefore will not need to detain us here; but a few words must be said with respect to each of the remaining four, if our sketch of the geography of the Empire is to make any approach to completeness.