This dissertation establishes the pivotal role of ecclesiastical architecture and its bureaucratic administration in forging modern, politically engaged publics in early nineteenth-century Prussia. It focuses on church building in the formerly French-occupied Rhineland, a large majority-Catholic territory on the Rhine river that was awarded to Protestant Prussia following the defeat of Napoléon in 1815. The differences between Rhenish provincials and their new Berlin overlords extended well beyond divergent confessional identities, as French occupation of the Rhineland from 1794 to 1814 had bestowed the region with a markedly more progressive economic, legal, and social character than its new Prussian rulers. One aspect of the Prussian government's desire to bring its newly acquired provinces into the state's hegemonic fold was the mandate that all new provincial architectural projects, including even modest village churches, be subjected to bureaucratic review and approval by the central government. Designs for Rhenish churches had to travel from local parish councils to the desks of bureaucrats in faraway Berlin, where Prussian state architect Karl Friedrich Schinkel (1781–1841) assessed the aesthetic merits of all public representational buildings. In Berlin, Rhenish church designs were subjected to often harsh critique, demands for modification, or outright rejection. Critically, my research revealed that this bureaucratic process of regulation did not function in the frictionless, top-down manner envisaged by Berlin, as scholars have long assumed. Rather, many Rhenish parishes actively resisted Berlin’s interventions, protesting its remotely rendered judgments and defying its orders, in protracted bureaucratic battles that often played out over a decade or more. The Prussian state’s top-down bureaucratic mandates thus had the effect of driving bottom-up engagement by Rhenish faith communities with the machinery of civil society. My study begins with the introduction of a novel theoretical framework to support the consideration of bureaucratic operations as a methodological apparatus for studying early nineteenth-century architecture, its publics, and its makers. The social, legal, and economic character of the Rhineland in the early nineteenth century is then reviewed, as is the history and operational structure of the Prussian state building bureaucracy, the Oberbaudeputation, from its establishment in 1770 until 1840. Two detailed case studies of Catholic and Protestant church building initiatives follow, demonstrating how Rhenish parishioners approached their bureaucratic interactions with the Prussian state largely as equals, confident in their right and competence to judge, criticize, and advocate for desired outcomes on architectural initiatives—even in dialogue with figures with a pan-European reputation like Schinkel. The final chapter examines Berlin's bureaucratic interventions to grow the Protestant church in its provinces, including generous financial support for building projects and the introduction of a standardized template, designed by Schinkel, for all Protestant village churches. In conclusion, this study argues that the Prussian bureaucratization of ecclesiastical architecture compelled members of the Rhenish public to serve as arbiters of their own interests vis-à-vis state power structures. Community-based participation in local church-building taught provincials the power to be had from projecting beyond the sphere of the parish. In this respect, my dissertation offers new and significant elements of a prehistory of the confessional activism that characterized the Rhineland from the famous movement to complete Cologne Cathedral (1842–1880) to the 1848 revolutions and beyond. This study also aims to take its place amid a growing body of scholarship that locates emergent modernities in sacred, often rural spaces, rather than the more familiar settings of secular urbanity.