Although Babylon did not reach the zenith of its power till Nebuchadnezzar made it his capital, everything leads to the supposition that, for many ages, it had been the seat of science and civilization, and had carried on an extensive intercourse with distant as well as with neighbouring nations. Highly skilled in astrology and in astronomical observations, to which the clearness of the sky and the brightness of the stars offered every encouragement, the Babylonians were, however, not familiar with either the science or practice of navigation; but that they, in connexion with the Chaldeans, possessed an over-sea maritime commerce when their power was at its height, may be inferred from the writings of Isaiah:[220] “Thus saith the Lord, your deliverer; For your sakes have I sent to Babel, and thrown to the ground all obstacles, and the Chaldeans, whose cry is in their ships.” While however they carried on a large inland trade in vessels of their own, their oversea commerce was most probably conducted by the Phœnician ships of Tylos, or by the Arabians. Indeed, Heeren,[221] quoting Agatharchides, shows that the merchants of Gerrha sent to Babylon in _their own ships_ the produce of India, as well as frankincense and other perfumes from Arabia Felix. Of these the consumption must have been enormous, for Herodotus states that no fewer than a thousand talents were annually consumed by the Chaldeans in the temple of Belus alone.[222] Besides, there was a large overplus, which was conveyed up the Euphrates to Thapsacus, and then distributed by caravans over the whole of Western Asia. [Sidenote: Caravan routes from that city, to Candahar,] While Babylon constituted the emporium on the river Euphrates, the city of Opis,[223] on the Tigris, a few miles above Baghdad, formed another centre of commerce, to which the merchants of Gerrha had, with much success, directed their navigation from very early times, until interrupted by the Persians. From Opis, an important caravan route lay across Mesopotamia to Aradus, near Tyre; while from Susa, taking first a northerly direction, there diverged another route almost due east to Candahar, and thence by one of the branches of the Indus into Cashmir,[224] running almost in a continuous line with the road through Asia Minor mentioned by Herodotus. This great eastern route has been fully described by both Strabo and Pliny, who derived their knowledge chiefly from the writings of the companions of Alexander. [Sidenote: Cashmir, Ecbatana, and, Peucela, on the Indus.]