Laser Scans Unveil a Network of Ancient Cities in Cambodia
SIEM REAP, CAMBODIA — For decades, archaeologists here kept their eyes on the ground as they tramped through thick jungle, rice paddies and buffalo grazing fields, emerald green and soft with mud during the monsoon season.
They spent entire careers trying to spot mounds or depressions in the earth that would allow them to map even small parts of Angkor, the urban center at the heart of the Khmer empire, which covered a vast region of what is now Cambodia, Thailand, Vietnam and Laos from roughly 802 to 1431. In modern times, little material evidence existed beyond a network of monumental stone temples, including the famed Angkor Wat, and the sprawling settlements that presumably fanned out around the temples long since swallowed up by the jungle.
But this year, the archaeologists Shaun Mackey and Kong Leaksmy were armed with a portable GPS device containing data from an aerial survey of the area that is changing the way Angkor is studied. The device led them straight to a field littered with clods of earth and shot through with tractor marks. It looked to the naked eye like an ordinary patch of dirt, but the aerial data had identified it as a site of interest, a mounded embankment where the ancestors of today’s Cambodians might have altered the landscape to build homes.
但在今年，考古学家肖恩·麦基(Shaun Mackey)与贡·里克斯米(Kong Leaksmy)配备了手提GPS设备，里面存储了这一带的空中勘测资料，一举改变了对吴哥古迹的研究方式。这种设备可以直接把他们引向一片满是土块和拖拉机痕迹的田地。肉眼看上去，这里只是一片普普通通的土地，但是空中勘测数据显示它是一处有价值的地点，是一处隆起的堤坝，柬埔寨人的祖先或许曾在这里改变地貌，建造家园。
Almost immediately after stepping onto the field, Mackey, his eyes glued to the ground, pounced on a shard of celadon pottery. Soon the team had turned up a small trove of potsherds and began taking copious notes.
“It’s not sexy, like a temple, but for an archaeologist it’s really interesting that we have this representation of cultural activity,” he said. He and Kong Leaksmy are part of a consortium of scholars called the Cambodian Archaeological Lidar Initiative, or CALI, which uses a technology known as lidar to shoot ultraquick pulses of light at the ground from lasers mounted on helicopters. The way they bounce back can show the presence of subtle gradations in the landscape, indicating places where past civilizations altered their environment, even if buried beneath thick vegetation or other obstructions.
“这不像寺院那么迷人，但是对于考古学家来说，这些文化活动的象征真的非常有趣，”他说。他和贡·里克斯米隶属于一个名为柬埔寨考古光学雷达行动(Cambodian Archaeological Lidar Initiative)的学者团，简称CALI，他们使用一种名叫光学雷达的技术，用直升机上搭载的激光器向地面发射极快的激光脉冲。它们反射回来的方式可以显示地面的细微变化，指示古代文明曾经改变过地表环境的地点，就算被厚厚的植被或其他障碍物所掩盖也能勘测出来。
The soft-spoken, fedora-clad Mackey, a 14-year veteran of fieldwork here, noted that before lidar’s availability, an accurate ground survey of archaeological features in the Cambodian landscape entailed years or even decades of work.
“We had hit a roadblock in terms of technology until recently,” said Damian Evans, the archaeologist who heads the initiative. “The vegetation was obscuring these parts of Angkor and other monumental sites. The lidar allowed us to see through the vegetation.”
The Secrets of an Empire
The result, Evans said, has been an unprecedented new understanding of what the Khmer empire looked like at the apex of its power, with lidar-generated maps revealing an intricate urban landscape stretching across several provinces of modern-day Cambodia, along with a sophisticated network of canals, earthworks and dams the Angkorians used to control the flow of water.
“It is pretty amazing,” he said. “The larger the temples are, the larger the urban infrastructure around it is likely to be, so they weren’t lost, in the sense that we assumed that they must be there. But, of course, that is an entirely different thing from being able to see it in incredible detail and how it works and how it functioned, how it evolved, the morphology of these places.”
The group is using the maps to make more targeted excursions into the field, “ground-truthing” the lidar data to ensure that it is accurate and to determine where digging might be useful. On a recent mission, Mackey barreled down a freshly paved road in a pickup truck driven by Kong Leaksmy.
Although the Khmer empire’s great stone monuments have endured for centuries, spawning a $60-million-a-year tourism industry and preserving information about the dynasty of god-kings who ordered their construction, the stuff of everyday life at Angkor, made from wood, mud, thatch and brick, has long since rotted away in the hot and humid climate. Almost nothing has been known about the lives of those who built the temples and served its rulers — who they were, how they lived, what they believed.
David Chandler, a professor emeritus at Monash University in Melbourne, Australia, and a leading historian of Cambodia, said the new lidar data was particularly exciting because it was providing more information than ever about how ordinary people lived in the Khmer empire.
“People imagined it was a city, but they didn’t know how to imagine it, because they didn’t know what it looked like, Chandler said. “Now they do.”
“This is where Angkorian research is going to go from now on: research into the people who built the temples, not the people whom it was built for,” he added. “It’s putting the population of the city back in view.”
Being able to see the true scope of the city has led to discoveries in other areas, too. Lidar has helped find the giant quarry field where most of the sandstone to build the temples was taken from, and has identified mysterious earthen spirals close to Angkor Wat and a few other temples that might have served aesthetic or religious purposes.
At a remote but massive temple called Preah Khan of Kompong Svay, which Khmer King Jayavarman VII used as a base to raise an army against invaders from the east, scholars had worked for more than a decade to determine what lay below the surface, with little success. They ultimately concluded that the area was not thickly settled. But the lidar data revealed a dense cityscape that even included the same spirals seen at Angkor Wat, and helped pinpoint areas for archaeologists to dig that had not been looted.
有一处偏远的巨大庙宇名叫孔蓬思维圣剑寺(Preah Khan of Kompong Svay)，高棉王国的阇耶跋摩七世(Khmer King Jayavarman VII)曾在这里组建军队，抵抗从东而来的侵略者，学者们研究了十几年，想判定地表之下究竟埋藏了什么，但一直没有什么成果。最终，他们确定这个地方没有密集的古迹。但是光学雷达发现了一片密集的城市景观，甚至有和吴哥窟附近一样的螺旋，它协助考古学家们定位出精确区域，以便发掘遗迹中尚未被劫掠的部分。
In other cases, what lidar has not found is just as revealing. At the temple Banteay Chhmar, on the Thai border, archaeologists had also struggled to find evidence of settlement. The lidar data confirmed this, leading Evans to conclude that it was not the center of a city but perhaps a temple or a garrison that saw only waves of temporary settlement.
Perhaps most crucially, the long-held narrative of the collapse of Angkor is being recast by lidar evidence. Based on stone inscriptions in the temples, scholars have long believed the empire fell in 1431 after its capital was sacked by an invading Thai army, and the population of the city moved closer to Phnom Penh, Cambodia’s current capital.
But when these areas were scanned, there was no evidence of an influx of refugees. This suggests that while there might have been a political schism in 1431 that induced members of the royal family to move closer to Phnom Penh, the vast majority of people stayed near Angkor and only gradually moved away.
This understanding is unfolding day by day as the research continues. At Site 305, for example, Mackey and Kong Leaksmy uncovered bits of water jars, showing that the area included households, and shards of blue-and-white Chinese tradeware dating from after the 1400s.
“This helps feed into the concept that Angkor wasn’t really abandoned,” Mackey said.
“When myth becomes such entrenched history, archaeology is a way of challenging the written record, particularly because history is often written by the powerful who give voice to their own agendas,” he said. “But the material remains.”
To Kong Leaksmy, a recent university graduate who used lidar data to write her thesis on a small temple called Banteay Sra, the takeaway was simpler.
“I can see many, many points that I cannot see just by eye,” she said of the new tool. “It’s amazing for me.”