This article is an attempt through prosopography to examine any form – either external, vertical or horizontal – that professional mobility is likely to take on in the 19th century among a profession of middle-level civil servants, the conducteurs des Ponts et Chaussées. It first describes the phenomenon : any aspect included, the professional mobility of conducteurs increases in the early years of the Second Empire, remains rather high until the 1880s, and then starts to decline. Then, it proposes to make a prism from this evolution with a view to try and historicize the connection between these civil servants and their careers. It ends with an invitation to reassess the unfairly reduced importance of professional mobility among the intermediary administrative services of the time.