In the Syriac Book of the Cave of Treasures, which in a general way we may reckon among the rewritten Bible texts, in ch. 27.6–11, an apocryphal fourth son of Noah appears, Yōnṭōn by name. This figure resides near the seashorein a far-easternland and possesses oracular and astrological wisdom. In 1980, Stephen Gero interpreted this figure against a Jewish background. Recently, however, Clemens Leonhard, following Witold Witakowski, has questioned this approach and denied any prehistory to Yōnṭōn; he regards him as an “invention” of the Syriac author of the Cave of Treasures. In the present article I aim to investigate whether it is possible indeed to trace a Jewish origin of Yōnṭōn's appearance in the Cave of Treasures. Taking Gero's interpretation as a starting point, I will first investigate the setting in which a figure like Yōnṭōn could have evolved within a Jewish context. Secondly, I will attempt to actually identify Yōnṭōn in earlier Jewish sources. In this I will follow a recent assertion of Su-Min Ri, that Yōnṭōn originates in the Biblical person of Yoqṭān (Gen 10:25). While Ri's assumption derives from the possibility of a misspelling, I will produce internal evidence which renders the identification of Yōnṭōn and Yoqṭān very probable, thus justifying the direction of thought taken by both Gero and Ri over against the allegations of Leonhard and Witakowski. Moreover, the following discussion will shed light on how Jews received influences from Hellenistic astronomy and astrology and how they read these concepts into, or set them in opposition to, the Bible.