Such are the chief geographical features of Assyria. It remains to notice briefly the countries by which it was bordered. To the east lay the mountain region of Zagros, inhabited principally, during the earlier times of the Empire, by the Zimri, and afterwards occupied by the Medes, and known as a portion of Media. This region is one of great strength, and at the same time of much productiveness and fertility. Composed of a large number of parallel ridges. Zagros contains, besides rocky and snow-clad summits, a multitude of fertile valleys, watered by the great affluents of the Tigris or their tributaries, and capable of producing rich crops with very little cultivation. The sides of the hills are in most parts clothed with forests of walnut, oak, ash, plane, and sycamore, while mulberries, olives, and other fruit-trees abound; in many places the pasturage is excellent; and thus, notwithstanding its mountainous character, the tract will bear a large population. Its defensive strength is immense, equalling that of Switzerland before military roads were constructed across the High Alps. The few passes by which it can be traversed seem, according to the graphic phraseology of the ancients, to be carried up ladders; they surmount six or seven successive ridges, often reaching the elevation of 10,000 feet, and are only open during seven months of the year. Nature appears to have intended Zagros as a seven fold wall for the protection of the fertile Mesopotamian lowland from the marauding tribes inhabiting the bare plateau of Iran.