The liturgy, the public worship of the Catholic Church, was a crucial factor in forging the society of early medieval Rome. As the Roman Empire dissolved, a new world emerged as Christian bishops stepped into the power vacuum left by the dismantling of the Empire. Among these potentates, none was more important than the bishop of Rome, the pope. The documents, archaeology, and architecture that issued forth from papal Rome in the seventh and eighth centuries preserve a precious glimpse into novel societal patterns. The underexploited liturgical sources in particular enrich and complicate our...