Hyrcania, an ancient country of Asia, comprising the western portion of the mountain region between the S. E. shores of the Caspian (sometimes called the Hyrcanian sea) and the river Arius (now Heri-rud). It consisted mainly of the valleys of the Nika, Gurgan, and Atrek. It was a most productive country, capable of sustaining a dense population, and deserving Strabo's description of being "highly favored of heaven." The Hyrcanians seem to have been a people of Turanian race, intermixed with Aryans. After a short resistance they submitted to Cyrus. When the Persian empire was organized by Darius Ilys-taspis into satrapies, Hyrcania was added to the satrapy of Parthia. After the Macedonian conquest, Hyrcania became a part of the empire of the Seleucidse. The Parthian king Arsaces II., or Tiridates, detached it from the Syrian empire and added it to his own territories. Shortly afterward it was invaded and devastated by Scythians. It was also invaded by Antiochus the Great, in his Parthian war, but seems to have remained unsubdued.

A subsequent revolt against the Parthian rule was unsuccessful.