Iran, a Middle Eastern country south of the Caspian Sea and north of the Persian Gulf, is three times the size of Arizona. It shares borders with Iraq, Turkey, Azerbaijan, Turkmenistan, Armenia, Afghanistan, and Pakistan.The Elburz Mountains in the north rise to 18,603 ft (5,670 m) at Mount Damavend. From northwest to southeast, the country is crossed by a desert 800 mi (1,287 km) long.Iran has been an Islamic theocracy since the Pahlavi monarchy regime was overthrown on Feb. 11, 1979.The region now called Iran was occupied by the Medes and the Persians in the 1500s B.C., until the Persian king Cyrus the Great overthrew the Medes and became ruler of the Achaemenid (Persian) Empire, which reached from the Indus to the Nile at its zenith in 525 B.C. Persia fell to Alexander in 331–330 B.C. and a succession of other rulers: the Seleucids (312–302 B.C.), the Greek-speaking Parthians (247 B.C.–A.D. 226), the Sasanians (224–c. 640), and the Arab Muslims (in 641). By the mid-800s Persia had become an international scientific and cultural center. In the 12th century it was invaded by the Mongols. The Safavid dynasty (1501–1722), under whom the dominant religion became Shiite Islam, followed, and was then replaced by the Qajar dynasty (1794–1925).