The region immediately to the east of the Caspian, bounded on the north by the old course of the Oxus and extending eastward to the neighborhood of Merv, though probably not including that city, was Chorasmia, the country of the Chorasmians.
Across the Oxus to the north-east was Sogdiana (or Sugd), reaching thence to the Jaxartes, which was the Persian boundary in this direction.

South of Sogdiana, divided from it by the Middle and Upper Oxus, was Bactria, the country of the Bakhtars or Bactrians.

The territory of this people reached southward to the foot of the Paropamisus, adjoining Chorasmia and Aria on the west, and on the south Sattagydia and Gandaria.
East of the table-land lies the valley of the Indus and its tributaries, at first a broad tract, 350 miles from west to east, but narrowing as it descends, and in places not exceeding sixty or seventy miles, across.

The length of the valley is not less than 800 miles.

Its area is probably about a hundred thousand square miles.