As Western Christendom expanded dramatically along its frontiers in the eleventh and twelfth centuries, Church leaders debated how to organize and administer newly captured diocesan lands. These questions were especially pressing in the Iberian Peninsula, where conquests ushered in piecemeal, multidimensional processes of consolidation and integration in which lay and religious authorities sought to establish ecclesiastical institutions to govern territories containing Christian and non-Christian populations.

In Diocesan Dominion, Thomas Barton examines these dynamics through the comparative lens of two neighboring dioceses, Lleida and Tortosa, each formed from conquered Muslim territory in the mid-twelfth century. Using rich archival records, Barton reconstructs how bishops and their clergy strategized to enhance their authority over diocesan lands by engaging with landlords, military orders, and monasteries. He observes that, while these litigants sometimes invoked authorities such as the papacy or lay rulers and appealed to rigid privileges or legal guidelines to help resolve conflicts, they usually formulated compromises, sharing jurisdiction and resources. Observing commonalities and contrasts among these cases, Barton demonstrates the locally contingent nature of episcopal authority and shows how Western Christendom developed variegated and flexible ecclesiastical administrative frameworks long before its early-modern globalization.

The first book in any language to reconstruct the postconquest history of the dioceses of Lleida and Tortosa, Diocesan Dominion challenges default assumptions about episcopal practices during the high and later medieval periods and will be essential reading for all scholars in the field.