This paper explores a series of doctrinal disputations held in early Islamic Egypt, and known through the Hodegos of Anastasius of Sinai (fl. c.670-700). Using the text’s prosopographical and contextual cues, it argues that these disputations occurred in the 680s, in the aftermath of Constantinople’s Sixth Ecumenical Council, the decisions of which had thrown the Chalcedonian Christians of the caliphate into conflict and schism. In 686 at Babylon, it is argued, Anastasius had confronted the famed Edessene and Severan Athanasius bar Gūmoyē before the Marwānid prince and governor ‘Abd al-’Azız, and there been defeated. That defeat is indicative of the new-found position of the Egyptian Severan Church, which now flourished under Marwānid patronage.