This article aims to shed light on the exchange of technical knowledge between architects, master craftsmen and workmen on building sites at the end of the eighteenth century. In the Age of Enlightenment, major building sites were places where a large number of skilled practitioners of various ranks met (engineers, architects, contractors, experts, craftsmen). These were therefore places where the exchange of knowledge and know-how occurred but also places of struggle for power and knowledge. The article examines these exchanges and struggles using the case study of the building site for the dome of the Halle au Blé in Paris (1782-1783).