Independence Monument; Vann Molyvann, architect (All photos: Luke Duggleby for The Wall Street Journal)

A lone figure walks the stands of Vann Molyvann’s Olympic Stadium.

The Chaktomuk Conference Hall, one of Mr. Molyvann’s earliest designs, was built in 1961.

The library at the Institute for Foreign Languages, now part of the Royal University of Phnom Penh

More of Mr. Molyvann’s work at the Institute for Foreign Languages

Yet more of the institute

Vann Molyvann, Cambodia’s greatest living architect, recalls that the night his Olympic Stadium in Phnom Penh was completed, in 1964, “I took my wife to see the work.” Sitting in the top tier of the stands, they listened to Dvorák’s “New World Symphony” over the stadium’s speaker system. “It was one of the great moments of my life.”

In the years after Cambodia won independence from France in 1953, Mr. Molyvann—then scarcely in his 30s—set out under the tutelage of King Norodom Sihanouk to transform Phnom Penh from a colonial backwater into a modern city. But in the late 1960s the country was drawn into decades of war and terror, including years under the murderous Khmer Rouge regime, and Mr. Molyvann’s vision was virtually forgotten. The architect himself had to flee the country.

And while he returned in triumph after more than 20 years abroad, it was to find that grand titles didn’t translate into influence in today’s Cambodia. His legacy—structures in a style dubbed New Khmer Architecture—lives on, contributing significantly to the flair of the city, but even that is in danger as Phnom Penh, like other Asian capitals, clears historic buildings to make room for skyscrapers.

Cambodia is best known for its magnificent temple ruins at Angkor, remnants of a great Southeast Asian empire that covered the country’s current territory as well as parts of Vietnam, Thailand and Laos. After Angkor fell to the Siamese in the 15th century, a new Cambodian capital was founded on the banks of the Tonlé Sap River. That city, Phnom Penh, remained an unstable settlement, caught up in the geopolitical ambitions of Cambodia’s more powerful neighbors, until the French arrived in the 1860s. The colonial administrators drained the neighboring swamps and created a grid street plan, dotted with sumptuous villas, Art Deco markets and impressive government structures.

Even then, Phnom Penh was modest, small-town colonial France—and when Mr. Molyvann received a scholarship from the colonial government and set off for the Sorbonne in Paris, it wasn’t with the dream of returning to remake it. He was a law student. But as he pursued his degree, and struggled with the compulsory Greek and Latin, he had an encounter that changed his life.

“I met Henri Marchal, the curator of Angkor for the École Française d’Extrême-Orient [the French School of Asian Studies],” Mr. Molvyann remembers, “and suddenly I knew I wanted to be an architect, so I changed to the École Nationale Supérieure des Beaux Arts, where I studied until 1950 under Le Corbusier.” He regards that modernist architect and designer as his greatest teacher.

After that, Mr. Molyvann stayed on in Paris for several more years, studying Khmer art. While he looks back fondly on the period, he is also keenly aware that some of Cambodia’s later traumas had their origins in the Paris of that time.

“The Khmer Rouge was born in the Latin quarter of Paris,” he says. As they debated their country’s postcolonial future, Mr. Molyvann says, the city’s 400 or so Cambodian students split between nationalists and Marxists. Khieu Samphan, whom he knew as a fellow Sorbonne student, would go on to become head of state in the Khmer Rouge government.

By 1956, Mr. Molyvann was back in Phnom Penh. Independence had broadened Cambodia’s horizons, in part thanks to the efforts of King Sihanouk, who at various times officially dropped his title to serve as prime minister, head of state or president, though Cambodians continued to refer to him as king. With tremendous energy and not a little royal eccentricity, the young monarch—also politician, artist, filmmaker, womanizer and host to a series of foreign heads of state and celebrities—worked to create a modern nation with an eye on the past. The leading members of an emerging urban elite, many of whom, like Mr. Molyvann, had returned from Paris, sought to create architecture, music, films, literature and art that married Cambodian tradition with modernist thinking.

Nowhere was this more apparent than in new administrative, public and private building projects that sprang up all over the capital—transforming Phnom Penh, within little more than a decade, into one of Asia’s most dynamic cities.

“It was difficult at the beginning, as Cambodians had never heard of architects,” Mr. Molyvann remembers. “All they knew were engineers and builders. There was a real dearth of qualified Khmer experts, as the French had used Vietnamese to administer my country. But within 10 years of independence the management of the country and its capital was Khmer. It was incredible.”

Mr. Molyvann was made chief architect for state buildings and director for urban planning and habitat in 1956 and given a number of ministerial posts in the following years. “I was designing the Independence Monument and was asked to present the king with a selection of marble,” he recalls. “I was too afraid to speak to him personally, but he made some suggestions and we got on perfectly after that.” Shaped like a lotus flower, the monument tower, completed in 1960, remains one of Phnom Penh’s landmarks.

Mr. Molyvann had part of the floodplain south of the Royal Palace drained and filled, and on this “Front de Bassac” constructed the country’s first high-rises, initially for visiting athletes for the 1966 Ganefo Games, a short-lived Asian alternative to the Olympics.

“We built the stadium for 60,000 people and surrounded it with a moat, so that the waters could run off in the rainy season,” he says.

Stefanie Irmer, whose KA Tours focuses on New Khmer Architecture, sees the relation between water and city as crucial to the architect’s vision for Phnom Penh. “Besides creating the ‘Front de Bassac’ area from wetlands,” she says, “almost every building Vann Molyvann designed was surrounded by water—to keep the termites out, but also to integrate the buildings into the flood plain.”

Many of Mr. Molyvann’s buildings are traditional in one sense—they are shaped like familiar objects. Chaktomuk Conference Hall, one of his earliest designs, is like an open palm leaf. The library of the Institute of Foreign Languages (now part of the Royal University of Phnom Penh) was inspired by a traditional Khmer straw hat. The lecture halls of the institute rest on sharply angled concrete pillars that give them the appearance of animals, about to jump. They are still in use today, as is the library.

By the early 1960s, for the first time in almost 800 years, Cambodia was blooming. The Angkor ruins were the region’s biggest tourist draw, and Phnom Penh had doubled in size and become a city others in the region admired.

But the politics were turning ugly. Norodom Sihanouk, serving as prime minister, began to suppress dissent. By the mid-1960s, the U.S. had combat troops in Vietnam; as American planes began bombing North Vietnamese positions in Cambodia, the country’s policy of neutrality became a farce. The former king’s repressive policies alienated the political left and some rural Cambodians, who began to join a shadowy communist movement, the Khmer Rouge. Meanwhile, the right and military had become fed up with his capriciousness and nepotism. When he left to visit China in 1970, a coup replaced him with army general Lon Nol. The Swinging ’60s, the meteoric rise of a young nation, the building boom in the “Pearl of Asia”—it was all over.

Mr. Molyvann remembers days with hard choices. “Shortly after Lon Nol came to power, the Israeli ambassador advised me to take my family out of the country,” he says; the ambassador, a friend of his, warned him about the crumbling security and the increasing persecution of those connected with the previous government. So when Mr. Molyvann left for a conference in Israel, with his wife, Trudy, and their six children, they didn’t return. Instead they moved on to Switzerland, his wife’s home country.

Five years later, the Khmer Rouge marched victoriously into Phnom Penh. The new rulers immediately emptied the cities, and for almost four years Phnom Penh was a ghost town. At least 1.5 million Cambodians, nearly a quarter of the population—Mr. Molyvann’s father among them—lost their lives in the killing fields. The fledgling intellectual elite was snuffed out.

“I had no contact during those years,” says Mr. Molyvann. “I had to give my children a new life, so we stayed in Lausanne.” He continued to work as an architect in Switzerland, Africa and Laos, for the United Nations and the World Bank. The Vietnamese pushed out the Khmer Rouge in 1979, but Mr. Molyvann “could not think of going back.” The new rulers ” were still communists.”

“It was not until 1993 that I returned—with the U.N.,” he says. Initially, his homecoming was triumphant. He was appointed minister of state for culture and fine arts, territorial management and urban planning and contributed to the application for Angkor’s successful recognition as a Unesco World Heritage site.

But he soon realized that the Cambodia he had left behind in 1970 no longer existed. Cambodian People’s Party leader Hun Sen, who had been installed by the Vietnamese and who continued as prime minister after the U.N.-organized elections, gave Mr. Molyvann back his villa, but the architect’s plans for Siem Reap—the province in which Angkor is located—were unappreciated. He had called for a “tourist village” set apart from both the temples and the old town of Siem Reap, integrated into the environment and with water conservation as a key goal.

“The government wanted to use the resources of Angkor to develop Siem Reap without the participation of the local people,” Mr. Molyvann says. “In 1998, I became president executive director of Apsara (Authority for the Protection and Safeguard of Angkor), the government body created to look after the temples. Three years later, I was fired.” Unchecked development in Siem Reap has led to a dramatic drop in groundwater levels, causing subsidence that has put the Bayon, one of the main temples in the Angkor area, in danger of collapse, according to experts from the Japanese Conservation Team for Safeguarding Angkor. Development has also driven up property prices and the cost of living, a hardship for the locals in a province that remains one of the poorest in the country.

But it was not just the government and developers standing against Mr. Molyvann and his vision. Bill Greaves, director of the Vann Molyvann Project, a nongovernmental organization engaged in recreating the lost plans of the remaining New Khmer Architecture sites, thinks postwar Cambodia is simply not aware of its past.

“Right now, Singapore and Shanghai are models for forward-looking cities, both for the government and the people,” he says. “Hence Phnom Penh’s different stages of history are likely to be discarded.”

In the past decade, as investment has begun to pour into the Cambodian capital once more, colonial and 1960s buildings have been replaced by chrome-and-glass edifices, floodwater lakes have been drained, local media have reported almost daily evictions and ministers have gushed over the need to build skyscrapers in order to keep up with the neighbors.

The government frequently declares that preservation has to go hand in hand with development. In practice, it seems to walk well behind. Beng Khemro, deputy director general at the ministry for land management, urban planning and construction, says his department’s hands are tied. “Many historical properties are in terrible condition,” he says. “The people who own them don’t understand the value of the past and would rather demolish them and build high-rises to make a profit. The past is not appreciated. Without a change in attitude amongst the population, we are fighting a losing battle.”

Cambodia has preservation laws, and Dr. Khemro says he is trying to pass a regulation to get them applied in particular instances. He’d like to try a pilot preservation project away from Phnom Penh, he says, noting that Cambodia’s second-largest city, Battambang, has many buildings from the French period.

“Also,” he adds, “there’s less pressure.”

Molyvann advocate Mr. Greaves is skeptical about the survival of the architect’s legacy. “The old buildings disappear at an alarming rate—even public edifices like the National Theatre, which was knocked down a couple of years ago, are not safe. We try and get there before the demolition crews arrive.”

A drive around town with Mr. Molyvann illustrates his curious position in this free-for-all scramble for change. At the Independence Monument, guards at first refuse him entry. Only after his driver reveals the distinguished visitor’s identity is the master architect, old and frail, allowed to climb the steps he designed half a century ago.

Passing the stadium, Mr. Molyvann looks at the haphazard development around his favorite creation. Appropriated by developers with government connections, the moat has been partly filled in to make space for shops and an underground car park; the result is annual flooding that threatens the entire sports complex.

With equal shades of sadness and anger in his voice, Mr. Molyvann says, “Today, it’s not the state who owns the old properties, but the ruling party, the CPP.”

—Tom Vater is a writer based in Bangkok.