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.
The northern portion, measured from the Alps at the Monte Viso to the mouth of the Po, has a breadth of about 270 m., while the maximum breadth, from the Rocca Chiardonnet near Susa to a peak in the valley of the Isonzo, is 354 m.
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.