Archaeologists have shed new light on an ancient city hidden in the Cambodian jungle that was once the capital of the powerful Khmer Empire. The empire ruled over vast swathes of Southeast Asia between around 800 and 1400 A.D.
The researchers say that the city, known as Mahendraparvata, represents an "enormous and remarkably early experiment in formal urban planning," being the first large-scale "grid-city" that the Khmer built. That's according to a study published in the journal Antiquity.
Mahendraparvata, is located in the Phnom Kulen mountain range, which consists of an elongated plateau in the northwest of the country, roughly 25 miles east of Angkor Wat—the spectacular temple complex and best-known relic of the Khmer civilization.
The temple is located within the ancient city of Angkor, which served as the capital of the Khmer Empire from the 9th century all the way through until its fall in the 15th century.
The available evidence suggests that Mahendraparvata was founded before Angkor, and that power was transferred to the latter city around 900 A.D. after the former was abandoned.
"The Phnom Kulen capital ruled at the end of the 8th century and first half of the 9th century," Jean-Baptiste Chevance, an archaeologist from the Archaeology & Development Foundation—Phnom Kulen Program, told Newsweek. "Radiocarbon dating results confirm this occupation, corresponding to the reign of [King] Jayavarman II."
Archaeologists had long suspected that an ancient Khmer capital lay hidden in the Phnom Kulen mountains but until now, archaeological evidence has been limited to a scatter of small and apparently isolated shrines, the researchers say.
One of the reasons for this is the fact that Khmer cities were mostly built with perishable materials which have not survived over the centuries. However, the region is also difficult to access, hindering research projects.
Not only are the mountains carpeted in dense vegetation that hides many of the ancient features, but the area is also dotted with landmines due to the fact that it was one of the last holdouts of the Khmer Rouge right up until the 1990s.
The Khmer Rouge ruled Cambodia for four years in the late 1970s, conducting a genocide that killed around a quarter of the population. Many of the mines that they planted remain unexploded today, making work in the area a hazardous business.
The first clues indicating the presence of an ancient Khmer capital in Phnom Kulen came from several historical inscriptions associated with King Jayavarman II, who was known to have unified and ruled Cambodia at the end of the 8th century and early 9th century, essentially kickstarting the Khmer Empire.
"The location of the city was unclear at the early stage of Khmer studies," Chevance said. "Mahendraparvata was first identified with Phnom Kulen at the beginning of the 20th century. It was not before 1936-38 that the first archaeological campaign revealed most of the brick temples and placed them, with their architectural decoration, within the chronology of Khmer art history."
"Apart from additional research in the 1960s completing the archaeological map, no other research was undertaken and the Cambodian Civil War left the mountain with no access for decades," he said.
Chevance and his colleagues began archaeological research at the site in the early 2000s, focusing on the main monuments—such as the pyramid-shaped mountain temple (the main marker of a Khmer capital,) other brick temples and some rock shelters.
"We identified the royal palace of the city, a vast complex of platforms and earthen dikes located on a central position linked with other sites," Chevance said. "Our archaeological research confirmed that these sites were dating back to the end of the 8th and beginning of the 9th century. There was therefore a stronger confirmation of the presence of this capital on the Kulen Mountain."
But due to the limitations of conventional survey and mapping techniques in the area, a coherent vision of the city itself remained elusive, the researchers say.
"The Ancient Khmer modified the landscape, shaping features on a very large scale—ponds, reservoirs, canals, roads, temples, rice fields, et cetera. However, the dense forest often covering the areas of interest is a main constraint to investigating them," Chevance said.
In recent years though, a revolutionary imaging technology known as LiDAR (Light Detection and Ranging) has emerged—which essentially lets you "see through" vegetation, enabling the archaeologists to work around some of the problems involved in accessing the area.
The technology makes use of instruments fitted onto aircraft that fire pulses of laser light towards the ground hundreds of thousands of times per second, enabling the creation of detailed 3D maps that reveal the topography of the land and any ancient man-made features.
Now, the team's latest LiDAR surveys, alongside ground-based research, have revealed thousands of archaeological features across an area of roughly 20 square miles. These features show what appears to be an advanced grid system that connects the various features of the city—such as dams, reservoir walls, temples, neighborhoods and the royal palace—helping to define its true layout.
The team even believe they have discovered evidence for subdivided city blocks due to the presence of numerous earthen enclosures that align roughly with, and often, about, the main linear "axes" or thoroughfares.
Even though Khmer cities were largely built with perishable materials, they have left, nonetheless, a durable legacy on the surface of the Earth, allowing archaeologists to trace their forms in the contours of the terrain, researchers say.
"The key finding of the study is the discovery of an urban network made of earthen dikes, hidden below the vegetation of Phnom Kulen," Chevance said. "The LiDAR technology allows us to 'see through' the canopy and reveal this vast network of earthen dikes—oriented east-west and north-south—composing a grid, defining the 'skeleton' of the city."
"After several excavation campaigns, the associated features such as plots and smaller dams can now be interpreted as settlements, an essential component for the definition of the city," he said. "Most of the previously known sites are linked with this network by their position and orientation."
According to the researchers, the latest study essentially confirms the hypothesis that Mahendraparvata was located on the Phnom Kulen plateau, and that it was the first capital of the Khmer Empire.
Furthermore, it yields new and important insights into the emergence of Khmer urban areas. They say that Angkor and other subsequent Khmer settlements used the urban plan of Mahendraparvata as inspiration.
The LiDAR survey also indicated that an ambitious engineering project to build a sophisticated water management system was left uncompleted. According to the archaeologists, the unfinished engineering work could hint at why the city may not have lasted long as the Khmer power center. However, they note that the reservoir built at Mahendraparvata may have inspired the artificial lakes that were central to the design of Angkor Wat.
The Khmer Empire had its roots in the early centuries of the first millennium, according to the researchers. However, it spread across Southeast Asia during what historians have described as the "Angkorian period," which stretches from the 9th to the 15th centuries.
"It was one of the most advanced civilizations in Southeast Asia, with strong political power, a very large and populated capital—Angkor, the largest capital of the pre-industrial world—and great architectural realizations," Chevance said.
One of the most mysterious features dotted across the Phnom Kulen plateau are the hundreds of 10-foot-high mounds arranged in geometric patterns. These remain a mystery to researchers, although it is thought that they were constructed after the majority of Mahendraparvata, the researchers say.