Lopez Lujan's team discovered a 13-ton stone monolith in October 2006, he said. The monolith was a rectangular, relief sculpture carved into a slab of pink andesite, a type of volcanic stone. Further excavation revealed that the sculpture depicted a female Aztec deity with curly hair, claws and visible teeth, wearing a short skirt, with arms and legs perpendicular to her body.
The form and positioning of the sculpture led Lopez Lujan and his team to suspect that it was meant to represent Tlaltecuhtli, an Aztec earth deity.
"Tlaltecuhtli literally means lord or lady of the earth," Lopez Lujan said.
Tlaltecuhtli has a "double role" in Aztec religion, he said. She is a nurturing and life-giving goddess, but she also has an insatiable appetite for blood, Lopez Lujan said.
"She also gulps down the sun each afternoon, regurgitating it at dawn," Lopez Lujan said.
Lopez Lujan showed several scans and pictures of the relatively flat, 3.7-meter sculpture.
Traces of pigment found on the monolith allowed the team to make an hypothesis about how the sculpture would have appeared in Aztec times, bathed in bright shades of red, black, blue and ochre, he said.
Tlaltecuhtli sculptures were often used as the bases of funeral pyres where the bodies of dead kings were cremated, according to the historical documents Lopez Lujan examined. This cremation ritual likely represented Tlaltecuhtli swallowing the bodies of kings at the end of their reign, in the same way as she would swallow the sun, he said.
"The metaphor for the king's reign is the sun's daily course," Lopez Lujan said.
Lopez Lujan and his team also recently discovered a large stone cactus sculpture beneath the corner of a bookstore in Mexico City, surrounded by underground electrical cables. According to Aztec legend, the Aztecs could gain their gods' favor by performing ritual sacrifice on top of cacti, he said.
Lopez Lujan hypothesized that the cactus sculpture, carved out of a single piece of basalt, was used as a base for Aztec sacrifice rituals. Lopez Lujan was able to discover the location of the sculpture after reading about the stone's potential existence in 18th-century historical records. Over the years, the stone became hidden underground, he said.
"It is clear that the stone remained hidden when many of the city streets were elevated to a higher level," he said.
Excavations of Aztec ruins buried beneath Mexico City are difficult, Lopez Lujan said, because modern asphalt and concrete cover the sites, Lopez Lujan said. The city also has a high water table and clay-like soil, making underground archeological projects more complex, he said. Many discoveries have occurred during construction projects, including during the construction of Mexico City's subway system, the installation of underground electrical wires and the paving of roads with cobblestones, Lopez Lujan said.
"These series of obstacles have meant that the excavation has progressed at the speed of an eye-dropper," Lopez Lujan said. "We have only a few pieces of a gigantic puzzle that we know we will never be able to assemble completely."
Lopez Lujan first began working for the Templo Mayor Project in 1980, when he was 16 years old.
"I called the director. I asked him if he wanted a slave to take out dirt," he said. "I'm still there after 29 years."
The lecture was co-sponsored by the John Sloan Dickey Center for International Understanding, the Robert T. and Catherine L. McKennon Fund and the Hood Museum of Art.
