<p> The Rue R&eacute;aumur, cleared and constructed between 1896 and 1900, was the first major urbanism project initiated in central Paris after the dismissal of Haussmann. Realized under the Third Republic and under the guidance of a democratically elected Paris Municipal Council, the street provoked an unprecedented public debate about urbanist priorities, the management of municipal debt, and architectural aesthetics. Disappointed with the visual homogeneity of the Haussmannian boulevard, Councilors liberalized building code and declared a Concours des Fa&ccedil;ades in the Rue R&eacute;aumur in order to visually revitalize their city.</p><p> That variation of the streetscape would turn on a monumentalization of the urban party-wall building through enlarged <i>saillies</i> and <i> avant-propos</i>, corbelled fa&ccedil;ade elements hitherto banned in the streets of Paris. Conceived as a central business district, the Rue R&eacute;aumur was also a unique concentration of commercial architecture, which encouraged an expanded use of iron structure to open building interiors and fa&ccedil;ades into naturally illuminated, floor-through spaces of manufacture. Construction in the Rue R&eacute;aumur was, then, guided by contradictory impulses. Charged with psychically countering the uniformity of the rationalized city, the exuberant elevations of the new street simultaneously masked a reordering of the architectural object by similar pressures towards economic and technological efficiency. </p><p> This dissertation treats the architecture of the Rue R&eacute;aumur and the public debate that shaped it as mutually determining engagements of architectural modernity. It situates the street's evolution as a response to the political, economic, spatial, and psychic challenges posed by the emerging capitalist metropolis. Reconstruction of the architectural and social discourses that informed design practice in the Rue R&eacute;aumur positions late-century eclecticism as an indispensable step in the development of interwar Parisian modernism. That architecture served as the primary object of rejection within modernist historiography and avant-garde theory due to its reliance on historical vocabularies. This study demonstrates that the perceptual immediacy desired of the late-century Parisian fa&ccedil;ade was of equal importance to the development of architectural modernism as theories of structural rationalism. It considers eclecticist architecture like that of the Rue R&eacute;aumur as a moment of dynamic invention within nineteenth-century theory and design practice, the terms of which would integrally condition Le Corbusier's reconception of architecture and architectural aesthetics a generation later.</p><p>