Bactria was the homeland of Aryan tribes who moved south-west into Iran and into North-Western India around 2500-2000 BC Later it became the north province of the Persian Empire in Central Asia.(Cotterell, 59) It was in these regions, where the fertile soil of the mountainous country is surrounded by the Turanian desert, that the prophet Zarathushtra (Zoroaster) was said to have been born and gained his first adherents. Avestan, the language of the oldest portions of the Zoroastrian Avesta, was once called "old-iranic" which is related to Sanskrit. Today some scholars believe the Avestan-Language was the western dialect of the Sanskrit because both languages are the oldest Indo-Iranian language of Aryans we know. With the time the Avestan-Language became developed by own western style.