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Zoroastrian

In Ancient Persia, incest between cousins is a blessed virtue although in some sources incest is believed to be related to that of parent – child or brother – sister. Under Zoroastrianism, royalty, clergy, and commoners practiced incest, though the extent in the lattermost class was unknown. This tradition was called Xwedodah (Avestan: Xᵛaētuuadaθa, romanized: Xvaetvadatha). The tradition was considered so sacred that the bodily fluids produced by an incestuous couple were thought to have curative powers. For instance, the Vendidad advised corpse-bearers to purify themselves with a mixture of the urine of a married incestuous couple. Friedrich Nietzsche, in his book The Birth of Tragedy, cited that among Zoroastrians a wise priest is born only by Xvaetvadatha.

To what extent Xvaetvadatha was practiced in Sasanian Iran and before – especially outside the royal and noble families ("dynastic incest") and, perhaps, the clergy – and whether practices ascribed to them can be assumed to be characteristic of the general population is not clear. There is a lack of genealogies and census material on the frequency of Xvaetvadatha. Evidence from Dura-Europos, however, combined with that of the Jewish and Christian sources citing actual cases under the Sasanians, strengthens the evidence of the Zoroastrian texts. In the post-Sasanian Zoroastrian literature, Xvaetvadatha is said to refer to marriages between cousins instead, which have always been relatively common. It has been observed that such incestuous acts received a great deal of glorification as a religious practice and, in addition to being condemned by foreigners (though the reliability of these accusations is questionable since accusations of incest were a common way of denigrating other groups), were considered a great challenge by their own proponents, with accounts suggesting that four copulations was deemed a rare achievement worthy of eternal salvation. It has been suggested that because taking up incestuous relations was a great personal challenge, seemingly repugnant even to Zoroastrians of the time, it served as an honest signal of commitment and devotion to religious ideals.