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This article focuses on the model of the Brunoy bridge, a late 18th century engeneering object, recently relocated to the École des ponts et chaussées. By reconstructing the circumstances and methods of its manufacture, as well as the uses to which this model was put until the early nineteenth century, the aim is both to highlight the plurality of its successive appropriations and to shed light on some characteristics of the administrative and scholarly world to which it belonged. Such a plaster artefact contributed to the design of a bridge over the Yerres and links up several social realms, highlighting practices which were far removed from the claimed ideal of general interest. Subsequently the object was exhibited and served to enhance the reputation of a man and a group of engineers. As part of the collections of the École des ponts et chaussées, it embodies a pedagogy centred on the study of models, and illustrates the part played by objects in the transmission of engineering knowledge and in the construction of the learned institution.