In the country of King Vishtaspa, the king and queen heard Zoroaster debating with the religious leaders of the land and decided to accept Zoroaster's ideas as the official religion of their kingdom after having Zoroaster prove himself by healing the king's favorite horse. Zoroaster is believed to have died in his late 70s, either by murder by a Turanian or old age. Very little is known of the time between Zoroaster and the Achaemenian period, except that Zoroastrianism spread to Western Iran and other regions. By the time of the founding of the Achaemenid Empire, Zoroastrianism is believed to have been already a well-established religion.