This chapter analyzes the Expiatory Temple of San Luis Gonzaga in Monterrey, an exceptional case of Neo-Gothic architecture in Mexico. Initially designed in 1898 by Italian architect Adamo Boari, the project was reconfigured and built by local engineers Genaro Dávila Caballero, Bernardo Reyes Ochoa, and Porfirio Treviño Arreola. Constructed between 1898 and 1923, the temple introduced the use of reinforced concrete for an ecclesiastical building—an unprecedented choice in Mexico at the time. The chapter situates this technical innovation within the broader industrial and symbolic context of Monterrey, a city marked by rapid modernization and a growing Protestant presence. The circular floor plan and Neo-Gothic vocabulary combined with modern materials reflected both ecclesiastical resilience and local industrial pride. The temple was promoted by Aurelia de Ochoa, wife of Governor Bernardo Reyes, and became an architectural response to liberal secularism and Protestant expansion. The building stands today as a unique synthesis of European stylistic reference, local engineering innovation, and political-religious symbolism, making it a true rara avis in the national architectural landscape.