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Iran is the ancient name of Persia, and it is derived from the root "Arya" or Aryan, the Indo-European branch of peoples who settled in that land. The Aryans of ancient Iran were Mazdayasni Zarathushtris, ie. Worshippers of Ahura Mazda (the name of God in Avestan) as revealed by the ancient prophet Zarathushtra, thousands of years before Christ.
However, all the ancient Zoroastrian scriptures speak of an earlier homeland from where our people came, the lost "Airyane Vaejahi" or seedland of the Aryans. From this homeland, the Indo- Europeans or Aryans moved to upper India, Iran, Russia and the nations of Europe such as Greece, Italy, Germany, France, Scandinavia, England, Scotland and Ireland.
Sanskrit, Latin, Avestan are all sister languages, and the present day upper Indian, Persian and European languages are related eg. Baradar in persian = Brata in sanskrit = Brother in english. "Persia" is actually a late European term for the land of "Farsi" language ie. Iran. The Arabic phase in Iran only began 1300 years ago, and we had to escape to India to preserve our Zoroastrian religion.
The "Vendidad" is one of the ancient scriptures of the Zoroastrians, actually called the "Vi-daevo-dat" or the law to fight against evil. In the first "Fargad" or chapter, the Golden Age of the ancient Aryans is outlined with their greatest king, "Yima Kshaeta" (Yam Raj in the Indian Vedas) who banished old age and death. Then, the ice age broke on the ancient home and the Aryans were forced to migrate southwards, to the southeast and the southwest.
Mr. Bal Gangadhar Tilak, a great Brahmin (Indian Aryan) scholar of India in the last century studied the Vedas and the Vendidad to find an ancient homeland of the Aryans. The Vedas are scriptures written by the Indo-Europeans or Aryans after they migrated to India. From the descriptions of the weather patterns mentioned in the Vedas, Tilak concluded that the ancient home must be in the Artic regions ie. above present Russia.
The Aryans migrated from the ancient home to Iran and from there to India and Greece and Europe. Tilak also said that the most ancient historical scripture was the Iranian Vendidad, which actually describes the ancient homeland of the Aryans, the Aryan King Yima Kshaeta who ruled over it (Yama Raja, lord of the underworld in latter day Indian Hinduism) and the onrush of winter, sent by ahriman (the devil) which caused the great migration. This is the famous first "Fargad" of the Vendidad which fascinated a lot of European scholars in the last century.
The ancient Aryans believed that the world as created by Ahura Mazda was perfect, with no evil. The first man Gayo Maretan had no disease, no illness, no hunger and thirst. Only the good creation of God existed eg., the Dog, Cow and Bull, Horse, Cock, Birds etc. Then ahriman the evil one attacked the world and caused evil to appear, disease and illness and old age, and the animals and the first man started to die. Night began to fall (before the sun was at the noon position - fixed, so there was no time). The evil brood of animals appeared eg. snakes, insects, and the cat breed. So evil in the ancient faith is an external introduction, which one day will be purged when the world will be bathed with the purification of fire - the latter also found in old German mythology. Paradise itself will be established on the earth, in the form of the Kingdom of Ahura Mazda. The English word "paradise" itself stems from the Avestan "PairiDaize", meaning the same. Also, the word "garden" probably stems from the Avestan "Garod-man" meaning the House of songs - the ancient name of heaven for the Aryans.
The Kings of ancient Iran were very proud to call themselves Aryans, their rock edicts indeed say so. "I am an Aryan, the son (Puthra) of an Aryan." This was righteous pride, because the word Aryan occurs time and again in the ancient scriptures of the Aryans - such as the Yashts (prayers to the divine elements) and the Vendidad (the law against evil).
About a time frame - today, many scholars tend to place Zarathushtra very late in time (around 1500 BC). The Greek historians at the time of Cyrus placed the first prophet at around 8000 years bc, that seems a more possible time to the former. However, the ancient Aryans were much sooner than that. Note that as per the Vendidad, Yima Kshaeta (King Yima) is the ancient king of the Aryans in the ancient homeland Airyanam Vaejahi (the seedland of the Aryans), and his memory is retained by even the Indian Vedas as Yama Raja (Yama King) because the Indian Aryans still remembered their ancient king after their split up in the migration, but they made him "Lord of the netherworld" later on.
Unlike the Indians, the Iranian Aryans still retained a perfect memory of days gone by -the perfect time in the ancient homeland, when Yiam banished disease, death and hunger from the homeland. This was indeed the true "Golden age" of humankind.