Religion and culture in ancient Iran
Religion and Culture in Ancient Iran refers to beliefs, activities, and cultural events in ancient Iran or olden Persia. It also makes reference to a combination of several Aryans and non-Aryan tribes. Aryans, or ancient Iranians, worshiped natural elements such as the sun, sunlight and thunder, but they eventually prayed to a single god. The Iranian ancient prophet, Zoroaster, reformed Iranian religious beliefs to a form of Henotheism. The Gathas, hymns of Zoroaster's Avesta, brought monotheistic ideas to Persia, while through the Yashts and Yasna, mentions are made to Polytheism and earlier creeds. The Vedas and the Avesta have both served researchers as important resources in discovering early Aryan beliefs and ideas. 
Early Heritage and First Settlement
Linguists and Anthropologists believe that several thousands of years ago, people from modern Europe, Iran, and India have common ancestors called Indo-Europeans. There are some theories concerning the origins of Indo-Europeans. Many Archaeologists are researching the causes of their immigration. Indo-Europeans slowly were divided into a multitude of tribes. One of these nations, named Aryans, moved eastwards and southwards to modern Iran and India. They founded several civilizations in Mesopotamia and the Indus river. The term Aryans refers to Iranians and Indians. Aryans who emigrated to Iran firstly took up residence by the Amudarya river in Central Asia. They gave their territory the title of Airyanem Vaejah which meant homeland of the Aryans, or Iranians as the term would later evolve.
Indo-Iranians were divided into more groups. This division undoubtedly occurred before the Iranian-Aryan emigration to the Iranian Plateau. As matter of fact, Indian-Aryans were housed in the whole of north west of India as well. Another group of Aryans who would be named Iranians immigrated to a territory between the Caspian sea and the Persian gulf. They consisted tiny tribes which independently settled down in scattered locations. A few notables of these Aryan tribes were the Persians and Medes. Their population gradually rose to the point where they could form new civilizations.
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