The ancient nation of Iran was historically known to the West as Persia until March 21, 1935. The name was used in the West due to the ancient Greek name for Iran, Persis. Persia is used to describe the nation of Iran, its people, or its ancient empire. The Persians have called their country Iran / Iranshahr since the Sassanian period. The name Persia comes from a region in the south of Iran, called Fars or Pars in the Persian language. Persis is the Hellenized form of Pars, based on which other European nations termed it Persia. Eratosthenes however does make mention of the word "Iran" in his writings. This region was the core of the original Persian Empire. Westerners referred to the state as Persia until March 21, 1935, when Reza Shah Pahlavi formally asked the international community to call the country by its native name, Iran, which means Land of the Aryans but because of some Persian scholars' protests the government announced in 1959 that both Persia and Iran could be used. (see Iran/Persia naming controversy). For the geography of Persia, see Geography of Iran. Once a major empire of superpower proportions [6] [7], Persia has been overrun frequently and has had its territory altered throughout the centuries. Invaded and occupied by Arabs, Turks, Mongols, British and Russians, and others -- and often caught up in the affairs of larger powers -- Persia has always reasserted its national identity and has developed as a distinct political and cultural entity. The first true empire of global proportions of Persia blossomed under the Achaemenids in (559 - 330 BC). The dynasty was founded by Cyrus the Great, who merged the various tribes and kingdoms into one unified entity. Following the Hellenistic period (300 - 250 BC) came the Parthian (250 BC - AD 226 ) and the Sassanid (226 - 651) dynasties. .