or Seistan
Extensive border region, eastern Iran and southwestern Afghanistan.
Most of its sparse population and about two-fifths of its area lie in Iran. It comprises a large marshland depression with a true desert climate. It is the reputed homeland of the legendary Kayānian dynasty of Persia and played an important part in Persian history, especially under the Safavid dynasty (1502–1736). In the 19th century it was the centre of a dispute between Persia and Afghanistan that led to the establishment of their modern frontier.