Diodorus, following Ctesias, declares that a number of cities were established from very ancient times on the banks of both the Tigris and the Euphrates, to serve as marts of trade to the merchants who imported into Assyria the commodities of Media and Paraetacene.
Among the most important of these marts, as we learn from Strabo, were Tiphsach or Thapsacus on the Euphrates, and Opis upon the Tigris.
It is from notices thus scanty, partial, and incidental, eked out by probability, and further helped by a certain number of important facts with respect to the commodities actually used in the country, whereof evidence has been furnished to us by the recent discoveries, that we have to form our estimate of the ancient commerce of the Assyrians.

The Inscriptions throw little or no light upon the subject.

They record the march of armies against foreign enemies, and their triumphant return laden with plunder and tribute, sometimes showing incidentally what products of a country were most in request among the Assyrians; but they contain no accounts of the journeys of merchants, or of the commodities which entered or quitted the country in the common course of trade.
The favorable situation of Assyria for trade has often attracted remark.
Lying on the middle courses of two great navigable streams, it was readily approached by water both from the north-west and from the south-east.

The communication between the Mediterranean and the Southern or Indian Ocean naturally--almost necessarily--followed this route.

If Europe wanted the wares and products of India, or if India required the commodities of Europe, by far the shortest and easiest course was the line from the eastern Mediterranean across Northern Syria, and thence by one or other of the two great streams to the innermost recess of the Persian Gulf.