Though engineers, architects and even landscape designers had staked out fields of operation for themselves in the seventeenth century such professions were in flux well into the eighteenth century. The same man might still operate in all of these fields. But by the middle of the century, professional boundaries were becoming clearer. Jean Rondelet took up his career in 1770, working for Jacques-Germain Soufflot, architect of the most conspicuous and structurally daring church of the period, Ste Genevieve, now known as the Pantheon, in Paris, Rondelet assumed the role of technical expert, taking on more and more control not only of the structural design but of the site organisation as well. And he was to dedicate his life to these tasks; for the church became a focus of structural debate that became increasingly partisan and acrimonious when faults in the structure threatened a total collapse of the dome. Architects and engineers found distinct voices for themselves in the ensuing uproar. Rondelet emerged, not quite the victor, but the man commissioned to ensure structural stability. This book, the first devoted to Rondelet, tells the story of the most celebrated architectural debate of the century. It also examines Rondelet's career in full, his publications and his long lasting influence on the training of architects and the administration of architectural practice in France. More than any other architect Rondelet represents the era of change during which the foundations for modern architectural theory and practice were laid.