Zoroastrismen, et annet av Jaspers' eksempler, er vesentlig for utviklingen av monoteismen. -- although Jaspers uses the Seleucid-era estimate for the founding of Zoroastrianism, which is actually the date of Cyrus' unification of Persia. The exact date of Zarathustra's life is debated by scholars with some, such as Mary Boyce, arguing that Zoroastrianism itself is significantly older. Others, such as William W. Malandra and R.C. Zaehner suggest that he may indeed have been an early contemporary of Cyrus living around 600 BC.