Part of our weekly "In Focus" series—stepping back, looking closer.

Deep in the jungle in the north of Guatemala, along deep-rutted 4×4 tracks, the pyramids of the great Maya city of Xultún are hidden under heavy vegetation and oddly symmetrical hills. But crudely cut tunnels in the sides of the hills signal a modern intrusion.

The tunnels are the work of "huecheros"—the local slang term for antiquity looters, derived from the Maya word for armadillo. On a building overlooking an ancient plaza, the looters scrawl a message, brazen and taunting: "We, the huecheros, stuck it to this place."

Almost every pyramid in the sprawling site has a looter's tunnel on at least one side. Most of the hieroglyphic panels, the pottery, and the jade from tombs here have been raided and sold on the black market to wealthy foreigners. One of the tallest pyramids—a majestic building that slices high in the air like the Temple of the Great Jaguar—was actually cut in half by looters, making it look like a giant stone napkin holder.

Xultún is part of an international trade in Maya antiquities that spread across much of the region in the 1980s and '90s and has scraped away what little opportunity was left to modern scientists to understand the people who once lived here. This amputation of cultural history—in many ways stretching back to the conquest of the New World—has left us with far more questions than answers about the Maya.

Looting continues to this day, though at a lower rate. Meanwhile, archaeologists, philanthropists, nongovernment organizations, and other leaders are grappling with the fallout from the country's cultural heritage being plundered for decades.

Xultún is not alone, nor is it terribly unusual. The Mesoamerican antiquity trade goes back almost to the Spanish conquest. In the beginning, Maya sites were spared from looting because they were mostly unknown, but by the 20th century archaeologists were working in the region and uncovering beautiful cities in southern Mexico and Central America.

This continued until the 1970s and '80s, when civil strife forced the scientists to abandoned the sites. The workers they left behind, now expert in locating ancient tombs, turned to the only work they had left to them—raiding untouched sites for things to sell on the black market. (Take our interactive Maya quiz.)

In Focus

It takes about four hours to get to Xultún from civilization. From Flores, a small tourist city on Lake Petén Itzá, the road starts out on pavement but quickly turns to gravel, then dirt roads, and then muddy 4×4 tracks. (See our interactive Maya map.)

In its heyday, Xultún was a major metropolitan center and powerful political player in the region. The city had flourishing art, culture, and religion. Today, it's little more than jungle pockmarked by the symmetrical hills—each covered in several feet of soil and stunted trees. The only clue that these hills were once pyramids surrounding a vibrant city center are the tunnels cut into their sides, exposing ancient building stones.

"The trench is left open, the rains get in, and the entire structure is destroyed," says David Lebrun, who recently created a documentary about Maya antiquity looting called Dance of the Maize God. "So you end up with a vase in someone's private collection, but you've destroyed the entire building."

Becoming a Huechero

Business for the huecheros accelerated as more people became fascinated with all things Maya while villagers were dislocated by the 1960-1996 civil war, which was most intense in the 1980s. One looter was Paulo Garcia (name changed to protect his identity). From a very young age, Garcia worked in the jungles of the Petén collecting chicle, a sap harvested from tropical trees and turned into chewing gum. In the 1970s he, like many others, became a huechero.

The most valuable items were panels with writing on them, statues, and sacrificial ceramic pots. Garcia says that although his fellow looters often brought good money into the community, they were a tough, lawless group. He tells one story of a friend who made an incredibly lucky find one day.

"He found 14 vessels," Garcia says. "That day he got sick with malaria, so the day after he told his friend that he wasn't coming to work. His friend left and then came back and shot him with his own rifle while sleeping, leaving him to die."

Later, Garcia claims, a few friends tracked the murderer down and repaid the favor. For their part, the end  buyers either were unaware or uninterested in how their pots came to their local art dealer.

"At the very beginning, when my collection was started, there was no consciousness of this issue of looting or not looting," says Fernando Paiz, a Guatemalan businessman who has collected Maya antiquities since he was a teenager in the mid-1960s. "It was just a collector trying to surround himself with pieces that were meaningful and important artistically or archaeologically."

Subsistence Diggers

Maya looting was fed by the desperation of Guatemala's long civil war and its aftermath. A polychrome pot might net a looter, or digger, $20 (U.S.) ($100 if it was very nice), while the final buyer might pay $10,000 to $20,000. David Matsuda, an anthropologist who lived among them for ten years at that time, estimated that there are several million such "subsistence diggers," with only a tiny fraction doing it full-time.

By then, the demand for pots, jade, and panels with writing on them was skyrocketing, along with people's fascination with the enigmatic Maya civilization. Museums across the United States and Europe clamored for anything Maya and didn't ask many questions about where they came from. The effects of all this digging have been devastating to archaeology, beyond just the damage to buildings.

"Any whole piece, or even reasonably whole piece, has almost certainly come from a burial or an offering," says Karen Olsen Bruhns, an archaeologist at San Francisco State University who works in El Salvador. "There are whole areas where people have had their history ripped out and sold in the United States and Europe."

For instance, the only way to find 14 Maya pots at once would be to uncover the burial of a very wealthy king. In archaeology, such finds can make a researcher's career and redefine our understanding of entire dynasties or eras during the Classic period (300-900 A.D.). But taken out of context, these pots are nearly worthless to science.

"It does almost nothing," says William Saturno, an archaeologist who has been working in Xultún for more than a decade and a National Geographic grantee. "It should be returned to the country of origin where it was taken from so that they might have it back. But it's unlikely that it will tell anything."

The practice of looting in the Petén has ebbed as Guatemala has stabilized and new avenues for making money have opened up for communities in the jungle (though looting is still rampant in other Central American countries). Yet, even today it's not hard to find modern huecheros.

Xultún was looted as late as 2001, and most community members know of at least one site being dug today. According to Matsuda, many of these looters work alongside drug traffickers to get their material north. At one of the Petén's biggest tourist destinations in May, one of the site's employees even offered to sell National Geographic a looted item.

Where It Goes

What has happened to all the looted material? Most of it has gone to unscrupulous museums or private collections.

Francisco Estrada-Belli, an archaeologist at Boston University who has spent his share of time cleaning up after tomb raiders, knows many collectors in Guatemala. Some are very careful with their treasures, but not all are.

"I was visiting my cousin and saw he had a polychrome bowl in his house—a pretty nice one. It was where he put his keys after work," Estrada-Belli says.

Paiz—whose family operated the largest supermarket chain in Central America, eventually bought by Walmart—has renounced buying looted Maya art and today helps fund legitimate archaeological digs. He's also trying to build a massive four-story museum that would subsume the current national archaeology museum and display both legitimate pieces and looted material.

"There are so many private collectors who do not trust the authorities to take care of their collections," he says. "They give me a very powerful argument: There is no place in Guatemala to put them. There's no decent place that will keep them properly."

Currently, he claims to have 3,300 looted pieces. Paiz says he no longer buys looted artifacts except in special cases overseas (he says 20 percent of his collection was retrieved from outside the country). The rest he hopes to get through donations. Still, the new museum has proved controversial among archaeologists. On the one hand, Guatemala deserves to have its relics back. On the other, it tacitly lets those who drive the destruction of cultural heritage off the hook.

The museum will cost an estimated $100 million (U.S.) and will house state-of-the-art facilities to preserve the artifacts. Paiz doesn't agree that looted material is worthless to science and points to various analyses that can reveal where a pot was made and how old it is, among other things.

85 Percent Fake

Bruhns says this is beside the point, since up to 85 percent of the pots on the market today are fakes. For stone carvings—which are nearly impossible to date accurately—that percentage may be higher. Undoubtedly many U.S. museums today display forgeries. Paiz acknowledges this problem and says one of the donors he visited had a collection that was 95 percent fraudulent.

Still, he says that in order for Guatemala to come to terms with its history, it needs to collect and preserve what it can. Plus, with such a facility, Guatemala can argue for repatriation of museum pieces—even if it means marginally feeding the illicit trade.

"I understand [the opposition's] point, and it's very difficult to argue against it. Because if there's no market, then there would be no looting," he concedes. "But when you have a choice of seeing a piece go and disappear from the country or be acquired by a foundation that exposes it to researchers and keeps it in the country, [you must choose the latter]."

Garcia, meanwhile, now works for a legitimate archaeological dig in the Petén, guarding the site against looters. He says he understands much better how different sites were connected and the larger story that the Maya have to teach us than when he was simply treasure hunting.

"[The money I earned looting] was all gone in women and beer. I never got to save anything," he says. "Now I am more relaxed because I am not working outside the law. I am working and the pennies I earn are earned honestly."