The richly decorated façade of the cathedral of San Martino in Lucca is both a masterpiece of Tuscan medieval art and a witness to the political and social developments of its era. Created between the late twelfth and the mid-thirteenth century, its rise paralleled that of Lucca as an independent city-state and the transfer of power from the city’s bishop to its citizens. This dissertation interprets the façade and its decoration as a direct response to these changes. It begins with a summary of San Martino’s history and a detailed examination of the documents pertaining to the cathedral opera, the administrative body overseeing the façade’s construction. Based on this material, it proposes that San Martino’s bishop and canons should be seen as the façade’s principal intellectual designers and shows how these individuals used this monument to maintain their institution’s centrality in Lucca’s public life and to overcome the internal divisions that threatened their city’s stability. Communicating through architectural form, intarsia, and sculpture, San Martino’s clergy encouraged Lucca’s citizens to understand their city as a sacred space, deployed ornamental imagery calculated to appeal to a broad swath of the population, and presented images of saints that served as models of both episcopal and lay behavior. Looking at San Martino in this way allows us to recognize the local character and originality of Lucchese art and architecture, as well as the interdependence of religious and political life in medieval Italy.