In the last known largely unexcavated Maya megacity, archaeologists have uncovered the only known mural adorning an ancient Maya house, a new study says—and it's not just any mural.

In addition to a still vibrant scene of a king and his retinue, the walls are rife with calculations that helped ancient scribes track vast amounts of time. Contrary to the idea the Maya predicted the end of the world in 2012, the markings suggest dates thousands of years in the future.

Perhaps most important, the otherwise humble chamber offers a rare glimpse into the inner workings of Maya society. (Video: "Mysterious Maya Calendar & Mural Uncovered.")

"The paintings we have here—we've never found them anyplace else," excavation leader William Saturno told National Geographic News.

And in today's Xultún—to the untrained eye, just 6 square miles (16 square kilometers) of jungle floor—it's a wonder Saturno's team found the artwork at all.

At the Guatemalan site in 2010 the Boston University archaeologist and Ph.D. student Franco Rossi were inspecting a looters' tunnel, where an undergraduate student had noticed the faintest traces of paint on a thin stucco wall.

The pair began cleaning off 1,200-year-old mud and suddenly a little more red paint appeared.

"Suddenly Bill was like, 'Oh my God, we have a glyph!'" Rossi said.

(Read Saturno's account of the Maya-mural discovery in National Geographic magazine online.)

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What the team found, after a full excavation in 2011, is likely the ancient workroom of a Maya scribe, a record-keeper of Xultún.

"The reason this room's so interesting," said Rossi, as he crouched in the chamber late last year, "is that ... this was a workspace. People were seated on this bench" painting books that have long since disintegrated.

The books would have been filled with elaborate calculations intended to predict the city's fortunes. The numbers on the wall were "fixed tabulations that they can then refer to—tables more or less like those in the back of your chemistry book," he added.

"Undoubtedly this type of room exists at every Maya site in the Late Classic [period] and probably earlier, but it's our only example thus far."

Maya Twilight

Its facade long ago erased by erosion and creeping plant life, the scribe's chamber was once part of a small building just off a massive Maya plaza circled by pyramids, where kings and high priests conducted ceremonies and peddlers likely sold the clay pots whose fragments now litter the forest site.

Discovered in 1915, the sprawling city was just five miles (eight kilometers) from another Maya metropolis, San Bartolo, which became famous when Saturno uncovered stunning, 2,000-year-old Maya murals there about a decade ago.

Beyond the two cities, the Maya civilization spanned much of what are now Guatemala, Belize, and Mexico's Yucatán region. Around A.D. 900 the Classic Maya centers, including Xultún, collapsed after a series of droughts and perhaps political conflicts. (Read about the rise and fall of the Maya in National Geographic magazine.)

The apparent desperation of those final years may have played out on the walls of the newly revealed room—the only major excavation so far in Xultún.

A "Different Mindset," Etched in Ancient Stucco

Despite past looting, the interior of the newfound room is nearly perfectly preserved.

Among the artworks on the three intact walls is a detailed orange painting of a man wearing white disks on his head and chest—likely the scribe himself, said Saturno, who received funding from the National Geographic Society's Committee for Research and Exploration and Expeditions Council. (National Geographic News is a division of the Society.)

Holding a paintbrush, the scribe is reaching out to the blue-feather-bedecked king, whose elaborate likeness was hidden behind a curtain attached to the wall by human bone, according to the study, published this week in the journal Science.

But what was really interesting was what the team found next.

Working with epigrapher David Stuart and archaeologist and artist Heather Hurst, the researchers noticed several barely visible hieroglyphic texts, painted and etched along the east and north walls of the room.

One is a lunar table, and the other is a "ring number"—something previously known only from much later Maya books, where it was used as part of a backward calculation in establishing a base date for planetary cycles. Nearby is a sequence of numbered intervals corresponding to key calendrical and planetary cycles.

The calculations include dates some 7,000 years in the future, adding to evidence against the idea that the Maya thought the world would end in 2012—a modern myth inspired by an ancient calendar that depicts time starting over this year. (Related pictures: "2012 Doomsday Myths Debunked.")

"We keep looking for endings," expedition leader Saturno said in a statement. "The Maya were looking for a guarantee that nothing would change. It's an entirely different mindset."

Though the idea of cyclical time is nothing new in Maya studies, team member Rossi added, the Xultún mural is by far the earliest known expression of the concept.

For example, he said while pointing to the ring number, "this is something we don't see again for over 500 years."

Now Is the Time

The Maya at Xultún were likely less concerned with the end of the world than the end of their world, according to Mayan-writing expert David Freidel of Washington University in St. Louis.

For ninth-century Maya, tabulating astronomical calendars to predict times of plenty was akin to gauging the stock market today, said Freidel, who wasn't involved in the new study.

When the Mural was made, the Xultún region was facing "a period of intense drought. In fact, cities were collapsing in various parts of the Maya world in this era," he said.

"The preoccupation of this king and his courtiers with astronomical calculation is not an arcane exercise. It has a very practical consequence for the people of the city of Xultún, which is, What the hell is going on with the economy?"

Xultún Discovery "Pretty Wild"

During tough times, the Maya looked to their leaders to divine the intents of the gods and appease them.

In turn, those rulers may have looked to the scribes, who many archaeologists believe used past events—in combination with mysterious, complex arithmetic—to predict the future.

As such, the newfound workroom could hold secrets into how the long-forgotten political system operated.

But for the scientists, the mural is also about the joy of discovery.

"To be uncovering glyphs and reading them right off the wall—to be the first one in 1,200 years to read something? I mean, it's pretty wild," Rossi said.

Sadly, we may never understand the full context of the workroom. Many of the glyphs are badly faded. Worse, the entire city of Xultún was looted clean during the 70s, leaving very little other writing or antiquities.

Because of this, and despite Xultún's obvious prominence in the Maya world, many archaeologists had written off the site.