The Thirteenth Tribe (1976) by Arthur Koestler argues that Ashkenazi Jews are not descendants of ancient Israelites, but rather of the Khazars, a Turkic people who converted to Judaism in the 8th century and migrated west from the Caucasus to Europe. Koestler suggests this creates a "thirteenth tribe" with Caucasian, not Semitic, origins. Koestler’s work was often interpreted as an attempt to undermine antisemitism by arguing that Jews were not descendants of Palestine, but it has been largely rejected by researchers in favor of genetic evidence tracing Ashkenazi ancestry to the Middle East.