On a June morning during the Formula 1 Grand Prix weekend, thousands of F1 fans and tourists flooded into Monaco, the postcard-sized principality on the French Riviera. Along the two-mile circuit, just after Turn 8, visitors milled about its newest neighborhood, Mareterra, a 15-acre luxury development built directly on the Mediterranean Sea.

Even walking along Mareterra’s waterfront plazas under the cantilevered Le Renzo—a 17-story residential tower designed by Pritzker Prize-winning Italian architect Renzo Piano to look like a fragmented vessel emerging from a shipyard—there is a clear view of the superyachts moored off the Mediterranean coast and the floor-to-ceiling windows of the high-rise apartments above.

“There’s a billion dollars’ worth of yachts in the bay, minimum,” says Bernard D’Alessandri, the general secretary of the nearby Monaco Yacht Club, looking out over a balcony. “And another billion here in the port.”

But the money spent on those superyachts pales in comparison to what buyers have dropped for homes in Mareterra. Every one of its 130 apartments and villas sold out before the neighborhood—which took 11 years and cost some $2.3 billion to build—was completed in December 2024.

The project was the brainchild of Monaco’s ruling head of state, Prince Albert II, and Patrice Pastor, a local real estate billionaire and Mareterra’s largest investor. From the beginning, it was designed to be an ultra-exclusive club even in the rarefied world of Monaco: Each one of the original buyers were personally interviewed and approved by Pastor and Guy Thomas Levy-Soussan, the project’s managing director. And would-be buyers could not offload those conversations to their assistants: “We refused to talk to any middlemen,” Levy-Soussan told lifestyle magazine Robb Report in 2023. “If you cannot spend one hour with us presenting the project to you, we’re not interested for you to live in this building.” (Levy-Soussan and Pastor both declined to speak with Forbes for this article.)

Now some of those original homes are already hitting the market at wildly higher prices less than two years after they were finished. Due to the project’s secrecy, there is no reliable data on the number of resales or even the average price. But some apartments are being offered at $12,900 per square foot, according to local brokers, a 33% premium compared to what some original buyers paid. (Monthly rents meanwhile go up to more than $130,000.) A 5,650-square-foot apartment in Le Renzo is currently on the market for $73 million, a price equating to about $12,990 per square foot, twice as expensive as even the toniest parts of Dubai. “We’ve had a wave of clients from Dubai,” says Silvio Piras, the managing partner of brokerage Piras Real Estate. “People want new, large and modern homes.”

Meanwhile the villas—including one listing for a 6-bedroom, 41,700-square-foot villa with such amenities as a wine tasting room, indoor and outdoor pools, a spa, sauna, massage room and private theater—are expected to break records. “These villas are so big that we're talking about more than 200 million euros [$230 million] as a starting price,” for ones with no water views, says Florian Valeri, the founder of brokerage Barnes Valeri Agency. For the seven villas on the seafront—the only homes built directly on Monaco’s coastline—prices could top $290 million, he says. Another broker predicts those will sell for some $350 million.

Some deep-pocketed buyers are holding out until they can acquire one of those seafront villas, no matter the price. “I have a client who asked about the villas in Mareterra, and so far there's just two on the second row,” says real estate broker Sufia Kiekbaeva at Magrey & Sons Monaco, who adds that she is aware of at least two villas and seven apartments currently up for sale in the neighborhood. “He's still asking me if I can find something on the [seafront].”

Despite all the secrecy, one high-profile sale at Mareterra has already smashed all previous property records around the world. In April, Bloomberg revealed that Ukrainian billionaire Rinat Akhmetov had purchased a 21-room, five-floor apartment atop Le Renzo for some $550 million in 2021, breaking the record for the most expensive home sale. The previous record was set by former billionaire Pan Sutong , who spent $319 million for a three-story home overlooking the Deep Water Bay golf course in Hong Kong in 2017. It’s also more than double the $240 million that billionaire Citadel CEO Ken Griffin paid in 2019 for his Manhattan penthouse, still the most expensive home ever sold in the United States. Akhmetov paid about $20,370 per square foot, roughly double the $10,420 per square foot Griffin paid and more than triple the average home price in Monaco of $6,200 per square foot—a figure that’s nearly double the next-most expensive city in the world, Hong Kong.

M onaco has long attracted the world’s richest and most famous—including Winston Churchill, Ringo Starr, Lewis Hamilton and of course Hollywood-royalty-turned-Monegasque princess, Grace Kelly—thanks to its Mediterranean shores and extremely friendly tax code. Smaller in size and population than Hoboken, New Jersey, Monaco is currently home to at least 29 billionaires worth a collective $167 billion, and another five members of the three-comma-club are investors in Mareterra or own second homes in the principality. Akhmetov’s reported neighbors at Mareterra include British chemicals billionaire James Ratcliffe and Formula 1 rivals Max Verstappen and Charles Leclerc , who live on opposite sides of Le Renzo.

Billionaires make up about 0.07% of Monaco’s 38,857 residents, making it the country—and city—with by far the most billionaires per capita in the world: one for every 1,340 people, more than its closest competitors, the Swiss ski resort town of Gstaad and the Cayman Islands in the Caribbean. And it’s growing more popular: Over the past year, Checkout.com founder Guillaume Pousaz and British billionaire developers Richard and Ian Livingstone all relocated to the tiny city-state. That number will likely increase, adds Piras, who says he’s seeing more demand from clients on the Forbes World’s Billionaires list for Mareterra.

Another big reason it’s long been a beacon for the rich and famous: It’s a renowned tax haven. Residents pay no income, inheritance, property or capital gains taxes (unless they’re French citizens). To become a resident, newcomers need to rent or buy a home—or manage a company that owns local real estate—and deposit 500,000 euros (about $580,000) into a local bank account. It’s also one of the safest countries in the world, with one police officer for every 70 residents.

“Mareterra came at a perfect time because international investors look for stability, security and long-term value,” says Ludmilla Raconnat Le Goff, the Monegasque government's delegate for attractiveness, tasked with enhancing the country’s appeal to foreigners. Pointing to the influx of new residents from Mareterra and the recent turmoil in the Middle East, she adds: “Monaco isn't only for people to come and live their best life at the casino. It's also for people who want to live a quiet, discreet life in a safe place.”

It’s safe enough that even billionaires take public transit: “I took the bus and saw Sir Philip Green on it,” recalls Russell Crump, a yacht broker, referring to the British retail billionaire whose wife and children live in Monaco.

The son of Grace Kelly and Prince Rainier III, Prince Albert II drew up plans to expand Monaco soon after he became the principality’s sovereign head of state in 2005. His father had spearheaded the last such expansion in the 1970s when he commissioned the construction of the Fontvieille neighborhood on land reclaimed from the sea. Unlike his father, Prince Albert’s vision was to build this one as an eco-friendly district constructed over the Mediterranean.

But the prince had to abandon the idea in 2009 following the global financial crisis and facing pushback over environmental concerns. He tried it again in 2013, this time choosing the name Mareterra—a portmanteau of the words for sea and land in Latin—to signify the bringing together of the two. His plan would extend the tiny principality’s territory by 3% to 0.8 square miles, adding about 15 acres. (As a percentage increase, that’s the equivalent of adding nearly the entire state of Oregon—or about two Mississippis—to the continental United States.)

It would also be enormously expensive. That’s where the private investors, who would cover the project’s costs while also giving the government significant tax revenues, came in. In 2015, the government signed a concession agreement with SAM L’Anse du Portier, a newly established real estate firm, to build Mareterra through private investment and the public works unit of Bouygues, a French engineering giant controlled by billionaire brothers Martin and Oliver Bouygues . The Bouygueses held 10% of the firm, with the remaining 90% owned by the similarly-named SCA Anse du Portier, the investment vehicle backed by private investors.

Under the terms of the deal, the project would be entirely financed by those investors, who would also keep all of the profits except for real estate sales taxes plus a $460 million lump-sum payment to the state. Unlike many other real estate developments, which include units reserved for Monegasque citizens, all of Mareterra’s homes and apartments could be sold on the free market.

A small group of local families and wealthy international financiers put up the capital. The largest was Patrice Pastor, a scion of the local Pastor real estate dynasty, whose roots date back to 1880 when his great-grandfather Jean-Baptiste moved to Monaco from northern Italy. Jean-Baptiste eventually built a successful construction company known for building many of Monaco’s high-rises as well as the seaside Larvotto district. The extended family, now split into several branches, is said to own some 15% of Monaco’s entire residential housing stock. Besides his 26% stake in Mareterra, Patrice owns dozens of properties in Monaco, London and the upscale village of Carmel-by-the-Sea in California, all part of an estimated $5 billion fortune.

Another prestigious family who invested are the Casiraghis, with a 10.5% stake. The family has been a fixture in Monaco since the 1980s when Italian socialite and businessman Stefano Casiraghi married Prince Albert’s older sister, Princess Caroline. Other real estate developers, including Patrice Pastor’s cousin Jean-Baptiste, the late Gerard Brianti (d. 2017) and the Lopez de la Osa family, plus Kazakh tycoon Bulat Utemuratov and the Swiss billionaire brothers Giammaria and Mario Germano Giuliani , all had 5% to 10% stakes as well.

The first step in building Mareterra was protecting and relocating marine species. Then in 2017 workers began dredging polluted sediment from the seabed. Next the developers built 18 enormous concrete blocks, known as caissons—each roughly 85 feet tall and weighing 11,000 tons—in Marseille, and then towed them across the Mediterranean to Monaco and installed them on an underwater embankment to form a protective seawall around what would become the 15 acres of new land. Work on the apartment buildings, villas, plazas and gardens began in 2020 and was completed in December 2024, about six months ahead of schedule.

Most buyers are thrilled. Either they love it so much that they have no plans to sell, or they are looking to make a substantial profit as prices and demand skyrocket. “If they doubled the size of Mareterra, it would still have been sold out,” says Irene Luke, co-managing partner of real estate brokerage Savills' Monaco office.

Investors may be even happier. The development generated more than $6.6 billion in total property sales, far more than enough to pay back the construction costs, a $1.2 billion bond plus more than $1.8 billion in taxes and concession payments to the Monaco government. According to previously unreported financial documents filed in Luxembourg by one of the investors, Mareterra’s development company reported a $3 billion net profit as of June 30, 2025—six months after the project was delivered—which was distributed to the investors as proceeds.

“When you deliver something of genuine distinction the market responds accordingly,” Utemuratov told Forbes . “Beyond the financial outcome there is real satisfaction in having supported a development that has become a landmark for Monaco and the region.”

The neighborhood has also strengthened Monaco’s allure to the most monied class, especially now that one of its top rivals, Dubai, has been drawn into the war with Iran.

“You don't pay tax [in Dubai] and it's easy to get residency, and you can open a bank account in three hours whereas here maybe it takes a month,” says Marilyn Schellino, sales director at brokerage Miells Christie’s. “But here there's stability. We'll never have Iran across the sea.”