According to these accounts, it appears to have gone directly east in about 36° N. latitude to Ecbatana, the capital of Media, and thence to the Caspian gates, through which everything coming from the west necessarily passed. On the north lay the Hyrcanian mountains; on the south an impenetrable desert; and on one portion of the route there was the narrow defile, about eight Roman miles in length, which Pliny describes as having been cut through the rocks.[225] From the Caspian Pass, the road led with various considerable turns till it reached Peucela on the Indus. From Alexandria in Ariis (Herát), and Ortospanum (Kâbul), other routes turned off into Bactriana, and thence proceeded into Great Tatary and Central Asia.[226] As there was considerable commercial intercourse between the neighbouring inhabitants of the city of Bactra (Balkh) and of Upper India, another route ran due north to Marakanda (Samarcand); and Heeren is of opinion that caravans traversed the desert from Badakhshan to Serica (China), and from that country to the Ganges. [Sidenote: Earliest land and sea combined routes.] Herodotus relates that from the Greek establishments on the Black Sea there were commercial routes through Central Asia, over the Ural Mountains to the country of the Calmucks of Great Tatary.[227] These different highways will be found laid down on a map, which has been prepared for reference (see Frontispiece), wherein will also be found the courses adopted by the vessels of ancient times in the navigation of the Asiatic seas, which, as far as can now be ascertained, was chiefly confined to the Arabian and Persian Gulfs, and the Indian Ocean. The periodical winds in these gulfs when once ascertained, rendered navigation comparatively easy, but, in navigating the Indian Ocean at the time of Alexander’s expedition, the monsoons were either not generally known to extend across the Indian Ocean, or were not made available to any great extent. Voyages, in the days of Herodotus, and for three centuries afterwards, were almost wholly of a coasting character. [Sidenote: Commercial efforts of Alexander in the East, and the impetus he gave to the development of the trade with India, by the erection of Alexandria, B.C. 331.]