The Marly-le-Roi Viaduct is a remarkable work of art inaugurated in 1884 to extend the Saint-Cloud - Marly railway line, which today runs on the Transilien L line (SNCF). It is a 283-metre structure with masonry and metal deck piles recently renewed (end 2018). The site is also remarkable. The structure dominates a once wooded valley and today largely urbanized. The viaduct strongly marks the site with its footprint. It is very clearly perceptible since the RN186 Route de Versailles and the Avenue de l'Abreuvoir which leads, as its name suggests, to the Abreuvoir, at the foot of the castle of Marly-le-Roi. This geographical positioning allows to put the work in perspective from the neighbouring reliefs, but also from the park and gardens of the Castle of Marly (classified Historical Monument). This context implies specific regulatory issues and a particular treatment in close collaboration with the Architect of the buildings of France of the sector. The work to renew the Marly-le-Roi viaduct allowed an architectural evolution of the work and is at the origin of the necessary requalification of the right-of-way works under the work. As part of the Civil Engineering contract, the spaces under the apron were mobilized and modified before being restored to their original state. These spaces span the entire length of the viaduct and an area of approximately 6,500m². The landscape project carried out in the continuity of the work on the viaduct allows a requalification of the impacted spaces with an objective of architectural and landscape quality as well as to place the project in its environment and to improve the living environment of the inhabitants. These developments have the objective of enhancing the urban and landscape ambiences while highlighting the approaches of the viaduct and proposing new uses. The landscape project thus includes the following types of development: - Creation of family gardens in restanques; - Development and quality of pathways and parking lots; - Management of erosion problems by the development of supports; - Securing the site through fencing and guardrails; - Plantations (trees/shrubs/perennials and grasses) and grassland planting;