[en] At least four Roman aqueducts serve Lyon/Lugdunum. After decades of constant monitoring by researchers from local Heritage Associations, the development of preventive archaeological surveys has led to better protection and adequate financial resources. During the research, the Brévenne aqueduct –particularly its buried sections– has delivered the most complete data, allowing the question of construction to be approached from different angles.Figuring out the steps of construction is an exercise that may seem dry, rather like the daily lives of the workers responsible for handling, shaping and assembling the canal's components. But this kind of analysis makes it possible to understand the marks left behind, breaks in different stages of the assembly or the manual practices of the builders. By focusing on construction standards, it is also possible to detect the specifics of a structure, its defects or anomalies and the range of technical solutions. A few anomalies also emerge, featuring installations that have disappeared. Ultimately, although none of the components of the canal adheres strictly to a single template, it remains a coherent structure, while water containment –particularly on this channel– is the main concern.This stratigraphic reading cannot be separated from the planimetric perspective, made necessary by the requirement to break down a large scale construction in order to handle uneven landscapes and to employ a variety of hydraulic engineering techniques. This multi-scalar sequencing of the work, first in large segments, then, at smaller scale in sections for construction and finally in a series of worksites and workshops, seems to be essential. The excavated remains must be understood in terms of this sequencing process.In this process, altimetry is the fundamental data point. To identify a spring with the capacity to channel water to Lyon at the expected height was a challenge in itself. Controlling the water route through topological changes and vegetation from the western surroundings of Lyon was another. This itinerary, which had to maintain certain milestones along the line for future stages of the work, involved several altimetric survey campaigns. Among these, the first was the one that concluded on the feasibility of the route, another entailed the laying of the floor of the installation trench and the last was dedicated to the foundations for the base of the specus.At this point, the legendary Roman regularity seems to have broken down. On the lengthwise profile of the segments, slopes and counter-slopes alternate continuously. However, the real anomalies are the short spans –often of about fifteen metres long, a hundred at the most– within the 70 linear kilometres that constitute the whole structure. Local scales do not fit well with the engineer's project. Ultimately, though, the contract was completed and the water reached Lyon.This presentation also raises questions about the position of this channel within Lyon's canal network. The Brévenne aqueduct was neither the first nor the last to be built, but it provided, around the middle of the 1st century AD, the highest flow available at an altitude never previously supplied. The standard of its construction also emphasises the containment of water at a level that would not be equalled in Lyon.On the other hand, its slope is less regular than that of the Gier aqueduct, since maintaining a sufficient height at the base of the flow is not its main concern. This canal starts very high and has to include drops in several places before it reaches Lyon-Fourvière. Flow management, the main source of abrasion, must have been a significant constraint for the builders. Should some of the anomalies in the slope be seen as intentional or not and what are the relative parts played by trial and error and calculation in this operation? More broadly, another question is whether a "technical memory" was maintained from one aqueduct project to another or was each one independent in its design, simply reflecting the skills and practices of the individual engineer? (Traduction de Mark Preston)

[fr] L'exposé des étapes de la construction d'un aqueduc romain, fondé ici sur celui de la Brévenne, s'appuie sur les données archéologiques issues de sites fouillés lors d'opérations d'archéologie préventive. Les moyens accordés à ces études mettent en relief la norme, mais aussi la spécificité de l'ouvrage dans le réseau d'adduction d'eau qui dessert Lyon/Lugdunum. Ce qui s'en écarte en révèle les anomalies, les malfaçons et les singularités, ces dernières étant souvent les indices d'aménagements érodés. La conduite de cette étude stratigraphique permet de constater in situ la complexité du travail accompli et d'admettre les compétences grâce auxquelles l'ingénieur a conservé toute la cohérence du projet. Cette approche permet également de saisir divers indices relevant d'une construction planifiée à différentes échelles, avec une partition du chantier en larges lots, puis en segments à construire et, au plus près des réalités du terrain, en une suite d'ateliers spécialisés avançant au jour le jour. La question de l'altimétrie, au cœur de la réussite de l'entreprise et si particulière sur ce tracé, y fait l'objet d'un développement spécifique. C'est finalement tout un projet qui se dessine et qui prend sa place pour plus d'un siècle au moins au sein du réseau lyonnais.