Ancient Iran, also recognised as Persia, is historic region of southwestern Asia that is only vaguely coterminous with modern Iran. The term Persia was used in the West chiefly for centuries, to label those regions where Persian language and culture prevailed, but it more fittingly refers to a region of southern Iran formerly known as Persis, alternatively as Parsa or Pārs, modern Fārs. Parsa was in fact the name of an Indo-European nomadic people who migrated into the expanse about 1000 BC. Parsa is for the first time mentioned in the annals of Shalmanesar II, an Assyrian king, in 844 BC. During the reign of the Persian Achaemenian dynasty (559–330 BC), the ancient Greeks first came into contact with the inhabitants of Persis on the Iranian plateau, when the Achaemenids—natives of Persis—were busy expanding their political sphere. The Achaemenids were the leading dynasty during Greek history until the era of Alexander the Great, and the use of the name Persia was slowly extended by the Greeks and other peoples to apply to the entire Iranian plateau. This tendency got reinforced with the rise of the Sāsānian dynasty, also native to Persis, whose culture dominated the Iranian plateau till the 7th century AD. The people of this region have traditionally referred to the expanse as Iran, “Land of the Aryans,” and in 1935 the government of Iran requested that the name Iran be used in place of Persia. The two terms, nevertheless, are often used interchangeably when referring to epochs preceding the 20th century.

The early history of Iran can be divided into three phases: (1) the prehistoric period, starting with the earliest signs of humans on the Iranian plateau (c. 100,000 BC) and ending approximately at the start of the 1st millennium BC, (2) the protohistoric period, covering the first half of the 1st millennium BC approx., and (3) the era of the Achaemenian dynasty (6th to 4th century BC), when Iran ventured into the full light of written history. The civilization of Elam (centred off the plateau in lowland Khūzestān) is an exception as written history started there as early as it did in neighbouring Mesopotamia (c. 3000 BC).

The sources for the prehistoric period are understandably wholly archaeological. Early excavation in Iran was quite limited, to a few sites. In the 1930s archaeological exploration amplified, but work got abruptly halted by the outbreak of World War II. After the war ended, interest in Iranian archaeology revived fast, and, from 1950 until archaeological study was summarily curtailed after 1979, numerous excavations transformed the study of prehistoric Iran.

Even for the protohistoric period historians are still forced to rely primarily on archaeological evidence, but much info comes from written sources as well. None of these sources, nevertheless, is both contemporary and local in relation to the events described. Some sources are contemporary but from neighbouring civilizations that were only loosely involved in events in the Iranian plateau—for instance, the Assyrian and Babylonian cuneiform records from lowland Mesopotamia. Some are local but uncontemporary, such as the traditional Iranian tales and legends that purportedly speak of events in the early 1st millennium BC. And some are neither local nor contemporary but are still valuable in reconstructing events in the protohistoric period (for instance, the 5th-century-BC Greek historian Herodotus).

For the study of the age of the Achaemenian dynasty, there is adequate documentary material and this period is regarded as the earliest in Iranian history for which archaeology is not the primary source of data. Contributing to the study of this epoch are, among other sources, economic texts from Mesopotamia Iran, and Elam; contemporary and later classical authors; historical inscriptions such as that of Darius I at Behistun (modern Bīsotūn); and later Iranian legends and literature.

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