Build on land reclaimed from the Mediterranean Sea, the Mareterra district has transformed a long stretch of Monaco's coast. (Photo Credits: Mareterra via CNN Newsource)

(CNN) — Known as a tax haven and playground for the rich, Monaco packs a population of around 39,000 — of whom almost seven in 10 are millionaires, according to property firm Knight Frank — into an area smaller than New York’s Central Park.

But the world’s second-smallest sovereign state has just grown by 3%.

New “eco-district” Mareterra, which has been built into the Mediterranean Sea, expands the microstate’s land mass by almost 15 acres. Inaugurated by Monaco’s Prince Albert II on Wednesday, the €2 billion ($2.1 billion) luxury development features a marina, seaside promenade and swathes of new high-end housing.

Le Renzo, a residential development designed by the celebrated architect Renzo Piano. (Photo Credits: Mareterra via CNN Newsource)

Announced in 2013, the extensive land reclamation project saw concrete chambers, or caissons, built in the sea before being drained of water and filled with 750,000 metric tons of sand.

Around half of the artificial landmass will be publicly accessible, with amenities including a park, cycle paths, a marina and shopping facilities. The district’s various green spaces have been planted with 1,000 trees imported from Tuscany, Italy.

Several high-profile architects were commissioned to create structures on the site. (Photo Credits: Mareterra via CNN Newsource)

New private residences on the site include more than 100 apartments and 10 palatial villas. Several high-profile architects, including Norman Foster and Tadao Ando, were commissioned to create structures in Mareterra. Italian architect Renzo Piano, best known for co-designing the Centre Pompidou, lent his name to the residential development building his firm designed on the site, Le Renzo.

While housing prices have not been disclosed, Knight Frank estimates that properties in the district will fetch around 100,000 euros per square meter (or more than $9,750 per square foot, almost twice Monaco’s average).

The new development features more than 100 new luxury apartments in one of the world's most densely populated places. (Photo Credits: Mareterra via CNN Newsource)

The development was privately funded, though Monaco’s government will benefit from a 20% tax on all property sales. The city state’s conference center, the Grimaldi Forum, was also expanded as part of the project.

Land is notoriously scarce in Monaco, which has a long history of building into the sea. Reclaimed land now accounts for more than a quarter of the principality’s territory. The most significant reclamation projects took place in the 1960s and 1970s, when the Larvotto and Fontvieille districts were expanded into the Mediterranean.

Earlier land reclamation efforts attracted the ire of environmentalists worried about the impact on Monaco’s marine life, which today includes 60 species of coral.

An aerial view of Mareterra, which is built on almost 15 acres of reclaimed land. (Photo Credits: Mareterra via CNN Newsource)

A more recent proposal was abandoned in 2009 due, in part, to ecological concerns raised by Prince Albert II, who is renowned for his work protecting ocean biodiversity.

Land reclamation in Monaco is now tightly regulated, and Mareterra’s developers said they took various steps to “minimize the impact on the natural ecosystem as much as possible.” The project’s website says planners consulted marine experts and created new habitats for fish, including artificial seagrass beds.

Developers also claim that 80% of heating and cooling in the district will run on renewable energy, including the power generated by more than 1.2 acres of solar panels.

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