The Northern and northwestern portion of the depression is occupied by the lake, a sheet of brackish water shaped like a horn (whence the modern name) measuring about thirty-five or thirty-six miles from end to end, and attaining in the middle a width of between five and six miles.

The area of the lake is estimated roughly at 150 square miles, its circumference at about ninety miles.

It has a depth varying from twelve to twenty-four feet.

Though the water is somewhat brackish, yet the Birket contains several species of fresh-water fish; and in ancient times its fisheries are said to have been exceedingly productive.
The principal cities of the Empire were, besides Pesargadae and Persepolis, Susa--the chief city of Susiana--which became the capital; Babylon, Ecbatana, Rhages, Zadracarta, Bactra (now Balkh), Maracanda (now Samarcand), Aria, or Artacoana (Herat), Caspatyrus on the Upper Indus,Taxila (Attock ?), Pura (perhaps Bunpoor), Carmana (Kerman), Arbela, Nisibis, Amida (now Diarbekr); Mazaca in Cappadocia; Trapezus (Trebizond), Sinope, Dascyleium, Sardis, Ephesus, Miletus, Gordium, Perga, and Tarsus in Asia Minor: Damascus, Jerusalem, Sidon, Tyre, Azotus or Ashdod, and Gaza in Syria; Memphis and Thebes in Egypt; Cyrene and Barca in the Cyrenaica.

Of these, while Susa had from the time of Darius Hystaspis a decided pre-eminence as the main residence of the court, and consequently as the usual seat of government, there were three others which could boast the distinction of being royal abodes from time to time, either regularly at certain seasons, or occasionally at the caprice of the monarch.