It lay on the ancient trade route from Sinope to the Euphrates, on the Persian "Royal Road" from Sardis to Susa, and on the great Roman highway from Ephesus to the East.
As a residence, however, for the rulers of the empire, a remote place in a difficult alpine region was far from convenient, and the real capitals were Susa, Babylon and Ecbatana.
Of these the Dora (called for distinctions sake Dora Riparia), which unites with the greater river just below Turin, has its source in the Mont GenÃ¨vre, and flows past Susa at the foot of the Mont Cenis.
Both in Persepolis and Pasargadae large masses of gold and silver from the tribute of the subject nations were treasured, as in Susa and Ecbatana.
So the Persian kings fixed their residence at Susa, which is always considered as the capital of the empire (therefore Aeschylus wrongly considers it as a Persian town and places the tomb of Darius here).