This paper presents a historical and analytical evaluation of the ribbed floor slab systems developed by the Italian structural artist Pier Luigi Nervi (1891-1979). The historical discussion includes the evolution of the floor slab from a non-structural element to an inspired structural system, culminating in Nervi’s patented ribbed floor systems. While the isostatic inspiration for the rib patterns of Nervi’s floor systems is well documented, the method used to generate these patterns is considerably unknown by comparison. The methods of experimental stress analysis identified by Nervi and the mathematical theories available prior to the 1949 isostatic floor system patent are discussed to clarify the means used to generate the isostatics. An Isostatic Line Tool developed for this paper is used to evaluate the correlation between the isostatics and Nervi’s arrangement of ribs for the Gatti Wool Factory, Palace of Labor, and Large Sports Palace floor systems. This tool can be used by designers in the conceptual design phase to develop ribbed floor systems inspired by Nervi.