Colorful murals buried for centuries in these ruins near Mexico City pose a mystery.
Who painted them, and when?
While more murals have been uncovered at other sites in Mexico, the detailed paintings here "are more well-preserved than is usual," says Joaquin Garcia Barcena, director of pre-Hispanic monuments of the National Anthropology and History Institute.
He said the paintings of a battle scene and two ancient priest-governors are also noteworthy for their naturalistic style.
Still more murals lie deeper in the seven layers of palaces built on a platform on the windy, 7,525-foot-high site. Archeologists found them while installing a huge orange roof to protect the site from rain, sun and dust.
They will be excavated when conservation work on the part now open to the public is complete, Garcia Barcena said.
Exactly who painted the 56-foot-long "Great Battle" and the two other murals remains a mystery.
Cacaxtla reached its peak between AD 650 and AD 1000, when a people known as the Olmeca-Xicalanca built a city fortified with dry moats and walls. They abandoned it around 1100.
With a population of 7,000 to 8,000, Cacaxtla was one of several capitals that emerged after the decline of Teotihuacan, a powerful city of 150,000 outside the present Mexico City that traded as far south as the Mayan cities in Guatemala.
There were earlier studies of the area, 40 miles southeast of Mexico City, but the murals were not discovered until 1975.
In one mural, a man with a Mayan profile wearing a bird headdress and bird claws for feet stands on a blue-plumed serpent.
On the other side of a doorway, a man in jaguar dress also stands on a serpent, holding spears dripping with water.
Both of the 7-by-8-foot paintings have borders of snails, turtles and other sea animals.
Garcia Barcena dates them to AD 850 to AD 900, other sources 100 years earlier.
"There was a zoological study to try to find if the sea animals were local or from the southeast, to see if they were influenced or painted by Mayas," Garcia Barcena says. "There was no conclusion."
In the "Great Battle," on either side of a stairway a level below, men in jaguar skins step on their defeated opponents. Again, they are men with Mayan features in bird dress. One man's intestines spill out of his body, another has an arrow through his nose.
In red, blue, yellow, black and white like the other two, it is believed to have been done 50 to 100 years earlier.
"The glyphs are not Maya," Garcia Barcena says. "For me, they must have been painted by people from nearby."
Small groups of Mayas and other ethnic groups lived in Teotihuacan, he said, and the artists may have been forced to do the paintings.
The murals are near the top of the layers on the 363-by-660-foot platform.
The Olmeca-Xicalanca covered some of the murals with straw, then with equally elaborate clay reliefs.
When they built another level, they knocked off tops of walls and filled in patios, protecting the murals for 1,300 years.
"What are unique are the palaces, that there was such a long sequence of remodeling," Garcia Barcena said. While building and expanding on a platform was common, "it is unusual that there were so many."
Built of dirt compacted with other materials such as volcanic gravel and covered with stucco, the structures also are vulnerable to the elements.
Builders ground seashells with sand to make the stucco, then gave it a shiny finish with the slimy juice of prickly pear trees that abound in the area.
The new 495-by-284-foot roof is second in size only to one over an archeological site in China, archeologists said.
A double layer of metal keeps out the rain, but critics say installation of the imposing structure damaged the ruins. It won't keep out the wind-blown dust and spoils the aesthetics, they say.
During installation of the roof, archeologists found a foot of volcanic ash halfway through the structures and are trying to learn which volcano it came from. They also discovered grain bins and three more murals.
Only 37 acres of the 642-acre site have been explored.
Overgrown mounds dot the landscape, each hiding more ancient structures, one of them a pyramid larger than the palace complex.
"We've been working here about 15 years, and to excavate we need another 50," said Sergio Guevara, an architect working on the project.