The Persian Empire was established by Cyrus the Great in the 6th century BCE. He allowed subject peoples to keep their own customs and institutions, and was seen as tolerant and law-giving. Darius the Great expanded the empire to its greatest extent, building Persepolis and establishing a taxation and road system. Zoroastrianism emerged during this time, teaching a dualistic battle between good and evil with Ahura Mazda representing good and Ahriman representing evil.