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The price of freedom is always high. When, in 1861, the principality of Monaco sought to ensure its independence, it ceded 95 percent of its then territory to France. Reduced to a tiny dot on the map, the sovereign city-state—which ceased taxing residents in 1869, thanks to the enormous income generated by its casino—expanded its territory seven times between 1907 and 2002. On each occasion, land was wrested from the sea, taking Monaco’s surface area to a total of 0.8 square miles. In December 2024, Prince Albert II inaugurated what may well be the principality’s last terrestrial expansion, a 15-acre neighborhood that increases its landmass by 3 percent. Baptized Mareterra—Latin for “sea and land”—the $2 billion development includes 10 villas, four townhouses, 110 very large apartments, underground retail and exhibition areas, and—a revolution for Monaco—2.5 acres of publicly accessible outdoor space.

Photo © Hufton + Crow, click to enlarge.

“One might consider that the best way to preserve our oceans would be to build nothing, either on the seabed or the coast,” admitted Céline Caron-Dagioni, Monaco’s minister of Public Works, the Environment, and Urban Development, at the Mareterra launch event. Monaco’s problem, she continued, is that its population is expanding—as, indeed, is the number of coastal inhabitants the world over. “If our goal is to create a harmonious cohabitation between humankind and the sea, we must invent solutions. They will never be perfect, but we must find the least harmful.” That was Monaco’s aim with Mareterra, which Caron-Dagioni hoped would stand as an example for similar projects in the future.

Master-planned by French architects Valode & Pistre following a 2013 design competition, Mareterra is the sequel to a far more ambitious Norman Foster–planned expansion that was dropped, say officials, because its environmental impact would have been too great. In place of the Dubai-style archipelago that Foster was tasked with producing, Mareterra restricts itself to the underwater coastal shelf, thereby preserving today’s marine currents. “At a depth of 115 feet, the isobathic curve follows the coastline as it was 8,000 years ago,” explains Denis Valode, founding partner at Valode & Pistre. “That gives Mareterra a very natural form. We also constructed a 40-foot-high hill, to avoid the artificial flatness of many land-reclamation schemes.”

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Incorporating trees and native plants intended to foster biodiversity (1), the district features generous swaths of open green space (2). Photos © Hufton + Crow

The first step in building this major piece of civil engineering was the creation of seafloor embankments, on which a series of giant concrete caissons were then laid, following the line of the isobathic curve. Each weighing 11,000 tons and rising above the waterline, the caissons are hollow, which helps dissipate the energy of stormy seas. The next step was to fill the space between them and Monaco’s existing coast with 827,000 tons of vibro-compacted sand (sourced in French and Sicilian quarries), through which hundreds of piles were then driven down to bedrock. Concrete foundations provide the base on which the neighborhood rises. Efforts to mitigate Mareterra’s environmental impact included removing fish trapped behind the caissons, replanting colonies of Posidonia oceanica, a Mediterranean seagrass that plays a key role in the marine ecosystem, and scraping the surface of the caissons’ high-resistance concrete to allow them to harbor sea life.

In its urban planning, Mareterra breaks with previous Monégasque practice in more ways than one. Not only is it far less dense, due to the open public space—an amenity unheard of in prior developments—but also because there are no skyscrapers. Building heights rise progressively from the three-, four-, and five-story villas in the northeast—two of which were designed by Tadao Ando, one by Foster, and another by Stefano Boeri—to the 18 levels of Le Renzo in the southwest, the flagship condominium conceived, as its name suggests, by Renzo Piano Building Workshop (everything else is by Valode & Pistre). While the villas, intended for billionaires, are essentially invisible from the public spaces, Le Renzo is the signature architectural project that gives Mareterra its identity. Pilotis-mounted, cantilevered, and aluminum-clad, it resembles the love child of Ron Herron’s avant-garde Walking City for Archigram and the consumer-economy extreme of behemoth cruise ships.

While Mareterra plays it very safe in terms of the accommodation it offers, the district does stand out in one respect: its landscaping. Designed by Michel Desvigne, it eschews the Riviera tradition of exotic ornamental gardens for something much more understated and ecologically serious. “It’s not merely a decorative backdrop,” declares Desvigne. “It’s a new piece of coastal territory, featuring all the plant species you would find in the Mediterranean,” from underbrush to the umbrella pine. With soil depths that are unusually generous for the circumstances, a residents’ charter that imposes the same species on Mareterra’s private gardens, and a continuity with the seashore planting of the next-door Larvotto quarter, a green corridor is formed that should attract indigenous fauna. Moreover, the public spaces are beautifully designed, with blond Burgundy stone, in both rough and smooth finishes, that forms pool beds, piazzas, and pathways, while the numerous aquatic features include a seawater swimming pool, a 2,600-foot-long stream zigzagging down the hill, and sheets of reflecting water on the land side of Le Renzo, where the neighborhood meets the old shoreline. If any aspect of Mareterra should serve as an example for the future, it surely is this.