Just prior to the rise of Islam in the sixth century AD, southern Arabia was embroiled in a violent conflict between Christian Ethiopians and Jewish Arabs. Though little known today, this was an international war that involved both the Byzantine Empire, which had established Christian churches in Ethiopia, and the Sasanian Empire in Persia, which supported the Jews in what became a proxy war against its longtime foe Byzantium.

Our knowledge of these events derives largely from an inscribed marble throne at the Ethiopian port of Adulis, meticulously described by a sixth-century Christian...