This article examines the complex historiography of the establishment of a Miaphysite hierarchy in Iraq in the early seventh century and proposes a reconstruction of the events themselves. As the Sasanian conquest of the Roman Empire progressed, the monastery of Mar Mattai in particular played a role in staffing and organising Miaphysites in conquered territory. Roman victories in 628 led to a complete reorganisation of the Miaphysite East, with the creation of Takrit as the premier centre for Miaphysites in Iraq and the official down-grading of Mar Mattai. Nevertheless, in practice, Mar Mattai continued to be a significant centre under the Umayyads.