The fourth century Ammianus Marcellinus (xxiii. 6. 32) identifies Zoroaster's patron with another Vishtaspa, better known as Hystaspes in English, the (late-6th century BCE) father of Darius I. The sixth century Agathias was more ambivalent, observing that it wasn't clear to him whether the name of Zoroaster's patron referred to the father of Darius or to another Hystaspes (ii. 24). As with the medieval Zoroastrian chronology that identifies Vishtaspa with "Ardashir" (see above), Ammianus' identification was once considered to substantiate the "traditional date" of Zoroaster.