jats:titleAbstract</jats:title> jats:p Study of the diplomacy between the Carolingians and the ʿAbbāsids has been hampered by the absence of any sources from the Caliphate commenting on their relationship. This paper identifies two variants of the Arabic Tiburtine Sibyl, apocalyptic prophecies composed by Syriac Christians in the early ninth century, that provide contemporary Arabic references to contact between Charlemagne and Hārūn al-Rashīd. In doing so, they shed new light on this diplomatic activity by indicating that it was considerably more important for the Caliph than normally appreciated. Combined with other references to the Franks in Arabic apocalyptic of the period, the evidence of these Sibyls suggests that Hārūn al-Rashīd accrued considerable prestige from his reception of Charlemagne’s envoys and the gifts that they brought with them.</jats:p>