Using picks, shovels, and high-tech forensic sleuthing, scientists are beginning to cobble together the grisly ancient history and fiery demise of Teotihuacán, the first major metropolis of the Americas.

The size of Shakespeare's London, Teotihuacán was built by an unknown people almost 2,000 years ago. The site sits about 25 miles (40 kilometers) north of present-day Mexico City. Temples, palaces, and some of the largest pyramids on Earth line its ancient main street.

Scientists believe Teotihuacán was the hub of trade and commerce in Mesoamerica until the city's civilization collapsed around A.D. 650. When the Aztecs stumbled upon the metropolis centuries later, they dubbed it the "City of the Gods," because they believed it was where the Gods met to create the present universe and sun.

Saburo Sugiyama, an archaeologist at Japan's Aichi Prefectural University, says recent excavations and analysis put a mortal face on Teotihuacán's mythological builders. The research is also providing clues to the city's final days.

"We are renewing the early history of Teotihuacán," he said.

One researcher investigating the site is Michael Spence, an anthropologist at the University of Western Ontario, Canada. He says a flurry of research activity at Teotihuacán since the 1980s is allowing scientists to understand the city's history. But "we still have a lot more science to work out," he added.

Tunneling for a Tomb

Sugiyama has concentrated his efforts at Teotihuacán's Pyramid of the Moon. The archaeologist has tunneled deep into the heart of the structure to search for the ruler thought to have ordered the pyramid's construction.

"We've not found the ruler's tomb yet, but we really feel we are very close to these people, the history, of who made this great pyramid," he said.

Sugiyama has made some intriguing finds, including dozens of beheaded people with bound hands. The bodies suggest bloody sacrificial rituals ripe with symbolism of military power, he said.

Excavations also reveal that the pyramid was constructed in seven stages, each stage an enlargement of the last. The work started in A.D. 100 and ended around A.D. 400.

Amid several sections, Sugiyama has uncovered the remains of sacrificed victims.

Analyses by Spence of the University of Western Ontario suggest the sacrificed victims came from outside Teotihuacán, possibly as captives brought back from distant territories or battles.

The clues come from oxygen isotopes in bones, which act as geological markers. "They tell you where a person was at a particular time," he said.

Climate and altitude are among factors that affect the isotopes. The isotopes found in remains of pyramid victims differ from those unearthed in city homes.

Bad Teeth

Spence has also found evidence that the health of Teotihuacán's population declined in the city's final century. Residents' teeth have tell-tale lines that form in childhood during episodes of severe stress, such as malnutrition or infection.

"Basically growth stops as the body concentrates on survival and repair," he said. "Then as the stress passes, the growth continues again. But there's a line left in the tooth that represents the stress episode."

Because teeth only grow during childhood, scientists can put a general age to when the stress happened. These signatures of bodily stress remain in adult teeth.

"We have shown that in the last century of the city there is a growing problem of some sort. We get more and more indications showing up in adult teeth," he said.

Teotihuacán's Demise

The largest unanswered questions about Teotihuacán concern its demise. Why, for example, was the city largely abandoned around A.D. 650?

The recent excavations are revealing new bits of information that help piece together an answer.

"We don't know exactly what happened at the final stage, but we know certainly the city was destroyed by man, not by natural disaster," Sugiyama said.

Researchers are uncertain whether insiders or outsiders caused the destruction, Sugiyama said, but they do know that the instrument was fire, particularly on Teotihuacán's monuments.

The archaeologist says an invading army could have set fires to the monuments as a signature of their conquest.

Spence, however, says the evidence suggests to him the fires were set during an internal revolt.

According to his theory, the deteriorating health of the city's poor was likely exacerbated by a drought or a disruption to the food supply. This spurred a revolution against the ruling elite and their symbols of power—temples, pyramids, and palaces.

"The destruction seems to have skipped the vast majority of the city and focused on the elite and punished the elite. That suggests a revolt to me," he said.