“Lest the Faithful Doubt or the Heretics Mock”: Patriarchs, Caliphs and Implementing Excommunication in the Jacobite Church c.650–850

This article considers the role of the Muslim authorities in enforcing Christian excommunication. After setting out late Roman precedents for the use of excommunication, it examines four cases in the period 650-850 in which the patriarch opposed other high-ranking clergy. It argues that Muslim authorities were increasingly willing to intervene in these disputes to support the legitimacy of the patriarch. The significance of this relationship is illustrated by the disintegration of the patriarch's to bring his opponents into line during periods of civil war, where the caliph's government was challenged.