In the context of a project to bring student life into the city centre, the northern French town of Amiens decided to convert its 17th-century citadel into a new campus for the Université de Picardie Jules-Verne. Several faculties regroup within the walls of Henri IV’s brick fortress, along with a host of public amenities and a huge park, opening up the area to the whole city. The citadel was completed in 1622 on the northern edge of the centre of Amiens. Occupying some 13 hectares (32 acres), the fortress has long constituted a major obstacle to development of the north of the city, which has occurred piecemeal, without strategy or infrastructure. It was recognised that the development of this site offered the opportunity to create a much-needed link between the city centre and its northern neighbourhoods, with far-reaching benefits for the overall urban development of Amiens.

The site presents various constraints: working around listed buildings, a variety of archaeological remains, as well as a complicated topography. But it also presented some key features to guide the project: the original clustering of buildings around a large, central space – the Place d’Armes; and the demolition in 1962 of most of the eastern side of the fortifications, opening up the site to the city. The new project takes the Place d’Armes as its starting point, the heart of the new campus, around which building is at maximum density. Among the existing buildings, three are preserved: the vaulted brick barracks along the northern edge of the Place; the stable block to the south; and the Governor’s Lodge, built above the listed 1390s city gate, the Porte Montrescu.

The Place d’Armes is laid with an extremely hardwearing surface of 6cm (2.4in) strips of terracotta interspersed with 2cm (0.8in) strips of grass. Developed specially for this site, the ‘diabolo’ system requires little maintenance and, crucially, can be laid absolutely horizontally as surface water simply soaks away (making it the first flat hard-core public square in the world). All the buildings on campus are rectangular in plan and take the 15m (49ft) height of the ramparts as their guide. Only one, the red ‘signal’ box, rises above.

The existing barracks building located on the northern length of the Place d’Armes are the main entrance into the university. The building also houses the university library and restaurant, and links via a public walkway through to the north plateau of the site. The building is accessed from the Place d’Armes via a series of footbridges crossing the (dry) moat, which is to be dug out to reveal the full height of the building’s magnificent brick arches, and glazed over to create library reading-rooms bathed in zenithal light. Behind the barracks, three new buildings are tucked into the hillside, creating a series of parallel rectangular volumes that are linked by a multi-level circulation structure. Fully glazed, this lightweight metal structure of stairs and footbridges give on to a succession of internal gardens between the four buildings.

At the west end of the Place, five lecture halls of varying capacities (from 150 to 479) are housed in a cluster of three volumes. In front of these, in pride of place as the focal point from the main, city-centre entrance onto the site, stand a little cuboid building made up of three superimposed boxes – the ultimate of which, a 23m-high pillar-box red periscopic metal box, provide a viewing point down to Amiens’ vast gothic cathedral. Known as the ‘signal building’, it looks set to be taken by one of the city’s brasseries for dining with a view.

The southern length of the Place is to be punctuated at its centre by a small covered space equipped for events such as small concerts, projections or debates. To its east is a new five-level administrative building, and to its west, the original stable block. Once renovated, the stable block houses large lecture halls (>100 sq m/ 1,076 sq ft) on the ground floor, with various general-purpose rooms, language labs and multimedia rooms on the two subsequent levels. The Governor’s Lodge accommodates administrative offices, as well as storage space, cloakrooms, public toilets and three two-level apartments for the campus caretakers. Up above the ramparts on the as yet undeveloped five-hectare (12-acre) northern plateau, a large sports centre is built, using the same language of form and materials as the rest of the project. It is across this area that pedestrian access to the campus and city centre is made.

All the buildings, both new and old, sit discretely beneath flat ‘living’ roofs. Looking down over the site towards the city centre from the northern plateau, the project resembles a series of planted terraces cut into the landscape.