The people of this area have traditionally referred to the region as Iran (Land of the Aryans) and in 1935 the government of Iran requested that the name IRAN be used in lieu of Persia. The two terms, however, are often used interchangeably when referring to periods preceding the 20th century. The early history of Iran may be divided into three phases:
The sources for the prehistoric period are entirely archaeological. Early excavation in Iran was limited to a few sites. In the 1930s archaeological exploration increased, but work was abruptly halted by the outbreak of World War II. After the war ended, interest in Iranian archaeology revived quickly, and, from 1950 until archaeological study was dramatically curtailed after 1979, numerous excavations revolutionized the study of prehistoric Iran.
For the study of the centuries of the Achaemenian dynasty, there is sufficient documentary material so that this period is the earliest for which archaeology is not the primary source of data. Contributing to the understanding of the period are, among other sources, economic texts from Mesopotamia, Elam (Ilam), and IRAN; historical inscriptions such as that of Darius I (the Great) at Behistun (modern Bisotun) contemporary and later classical authorsand later Iranian legends and literature.