In response to its economic and demographic growth, Monaco has decided to adapt its urban development to its limited space. Owing to the lack of available land, it is gradually extending into the sea. This will result in the creation of Monaco’s first eco-neighbourhood, Mareterra, comprising luxury homes and shops, enlargement of the Grimaldi Forum, a public car park, and public gardens, spaces and facilities. The maritime infrastructure, which will allow this new neighbourhood to be developed, consists of a fill enclosed by a band of 18 reinforced concrete caissons placed on an underwater foundation. To create this offshore extension, Bouygues Travaux Publics developed brand new construction methods that aim to reduce the environmental impact of construction works and protect Monaco’s natural marine heritage. Located between two reserves registered as protected marine areas (the Larvotto reserve and the Spélugues coral reef), the maritime infrastructure work was closely monitored by the Principality. Taking on board the conclusions of an environmental impact study conducted with its partners, Bouygues Travaux Publics designed each aspect of the project with this in mind.