Ardashir I was an energetic king , responsible for the resurgence not just of Persia but of Iranian-speaking peoples as a unified nation , the strengthening of Zoroastrianism , and the establishment of a dynasty that would endure for four centuries . Ardashir I was an energetic king , responsible for the resurgence not just of Persia but of Iranian-speaking peoples as a unified nation ( ethnous as it appears in the Greek version of his successor 's inscription on the Ka ` ba-ye Zartosht ) , the strengthening of Zoroastrianism , and the establishment of a dynasty that would endure for four centuries .