Etymology
In former ages, the names Aryânâ and Persis were used to describe the region which is today known as the Iranian plateau. The earliest Iranian reference to the word (airya/arya/aryana etc), however, dates back to the Iranian teacher Zoroaster (est. anywhere between 1200 to 1800 BCE, according to Greek sources, as early as 6000 BCE and is attested in non-Gathic Avestan; it appears as airya, meaning noble/spiritual/elevated; as airya dainhava (Yt.8.36, 52) meaning the "land of the Aryans" and as airyana vaejah, "the original land of the Aryans."
During the Achaemenian dynasty (550-330 BCE), the Persian people called their provincial homeland Pârsa, the Old Persian name for Cyrus the Great's kingdom, which belonged to the Persian tribe of the Iranian branch of the Indo-Iranians and which is retained in the term "Pars" or "Fars" (from which the adjective "Farsi" is derived). It is part of the heartland of Iran and is identified in historical maps, such as Eratosthenes's, and in modern maps.
The word Ariya is also attested in the Inscriptions of Darius the Great and his son, Xerxes I. It is used both as a linguistic and an ethnic designation. Darius and Xerxes refer to these meanings in the Behistun inscription (DBiv.89), which is written in a language referred to as airyan, or more commonly as Old Persian. Both Darius and Xerxes state in inscriptions at Naqsh-i Rustam (DNa.14), Susa (DSe.13), and Persepolis (XPh.13):
“ Adam Pârsa, Pârsahyâ puça; Ariya, Ariya ciça... I am Persian, son of a Persian; an Aryan, from an Aryan lineage.
”
In Parthian times (248 BCE – 224 CE), Aryanam was modified to Aryan. In the early Sassanid Period (224–651 CE), it had already evolved to Middle Persian Ērān or Ērān Shahr which finally resulted in New Persian Iran or Iran Shahr. At the time of the Achaemenian empire, the Greeks called the country Persis, the Greek name for Pars (Fars), the central region where the empire was founded; this passed into Latin and became Persia, the name widely used in Western countries which causes confusion as Persia is actually Pars (Fars) province. On 21 March 1935, Reza Shah Pahlavi issued a decree asking foreign delegates to use the term Iran in formal correspondence in accordance with the fact that "Persia" was a term used for a country called "Iran" in Persian. (see Iran naming dispute). The 1979 Revolution led to the current name Islamic Republic of Iran, but the nouns Persia and Iran, and the adjective Persian are still used.