An in-law of Cyrus and a Zoroastrian, Darius ruled the Persian Empire from 521-486. He expanded the empire west into Thrace and east into the Indus River valley -- making the Achaemenid or Persian Empire the
largest ancient empire. Darius attacked the Scythians, but he never conquered them or the Greeks. Darius suffered a defeat in the Battle of Marathon, which the Greeks won. Darius created royal residences at Susa, in Elam and Persepolis, in Persia.
He built the Persian Empire's religious and administrative center in Persepolis.