sentences:  As has been judged from the archaic context in which Tishtrya appears in the texts of the Avesta, the divinity/concept is almost certainly of Indo-Iranian origin.In a hymn of the Avesta (incorporated by Ferdowsi, with due acknowledgement, in the Shahnameh), Tishtrya is involved in a cosmic struggle against the drought-bringing demon Apaosha.According to the myth, in the form of a pure white horse the god did battle with the demon who, in contrast, had assumed the form of a terrifying black horse.