The fourth and fifth centuries CE were a crucial period in the development of Christianartistic, architectural, and liturgical traditions. Powerful patrons made available significant material resources and tremendous creative energy, facilitating the rapid development and proliferation of Christian churches and related spaces across the Late Roman Empire. Welleducated, connected clergy and elites brought considerable intellectual training and rhetorical skill to bear on Christian liturgical rites and homiletic traditions and contributed to a range of already thriving para-liturgical and private pious devotions. Comprised of 13 case studies spread across Rome, Milan, and Ravenna, this dissertation considers churches, baptisteries, and chapels, as well as the range of liturgical, para-liturgical, and private pious practices those buildings hosted. The project it embarks upon is two-fold: an interpretative reconstruction of pious practice, and an examination, through case studies, of the religious art, architecture, and artifacts that served, described, animated, suggested, and focused those practices. Recasting the familiar categories of Christian art and architecture as ‘technologies,’ it analyzes how these confluences of performative, somatic, visual, and spatial technologies impacted worshipping subjects toward a range of social, political, ecclesiastical, and even spiritual ends. Drawing upon recent insights from lived, material, and affective approaches to religion, it raises questions like how the frequent liturgical viewing of complex church mosaics differed experientially from the one-time encounter with a densely decorated baptistery during the highly charged Christian baptismal ritual. This dissertation engages many of the great churches and visual displays of the period, posing new questions to yield fresh insights from a familiar corpus of material.