MEXICO CITY — Mexican archaeologists say they have determined that the ancient Mayas built watchtower-style structures atop the ceremonial ball court at the temples of Chichen Itza to observe the equinoxes and solstices, and they said Friday that the discovery adds to understanding of the many layers of ritual significance that the ball game had for the culture.

The structures sit atop the low walls of the court, where the Mayas played a game that consisted, as far as experts can tell, of knocking a heavy, latex ball with their elbows, knees or hips, through a stone ring set in the walls.

The bases of the structures – essentially, look-out boxes set atop the walls, each one with a small slit running through it _had been detected before, but archaeologist hadn't been sure what they were used for. Since the ball court was built around 864 A.D., the boxes and the stairs leading to them had crumbled.

The government's National Institute of Anthropology and History announced Thursday that the boxes had been 90-percent reconstructed, based on the stone footings that remained. Late last year and early this year, a team led by archaeologist Jose Huchim confirmed that the sun shone through the slit-like openings when the setting sun touches the horizon at the winter solstice.

The sun's rays also formed a diagonal pattern at the equinox in the slit-like openings, which are about tall enough to stand up in.

Huchim said he knew of no similar structures at other Mayan ball courts. "This is the place where we're finding this type of pasaje (structure)," Huchim said. He said a stone structure atop a ball court at the nearby ruin site of Uxmal appeared to have been used as a sort of spectators' stand for elite audiences.

Huchim said the slits may have been used to determine when ball matches were played, given that the ball itself, as it was knocked through the air by the players, may have been seen as imitating the sun's arc as it passed through the sky.

It may have also been used "like a calendar, to mark important periods for agriculture," like planting the core crop of corn.

Finally, Huchim noted that old descriptions of the ball courts sometimes depicted people atop the walls, and that they may have been acting as umpires in the game.

Huchim said Thursday that stairways to the structures are being restored so visitors can observe the phenomenon.

Boston University archaeologist Francisco Estrada-Belli, who was not involved in the project, said the solar sighting lines were part of "part of Maya architecture and cosmology."

"The fact that the sun rise can be observed behind a structure should be understood in that sense, as reverence to the sun or other star, not necessarily as an observatory in the technical sense," Estrada-Belli said. The orientation of the structures "emphasized the sacrality of the ritual space."

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  • "Younger Brother Obsidian," as labeled on the north wall of the Maya city's house by an unknown hand, was painted in the 9th century A.D. Archaeologist William Saturno of Boston University excavates the house in the ruins of the Maya city of Xultún. Younger Brother Obsidian may have been the town scribe. Excavation and preservation of the site were supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic

  • Trees grow atop a newly discovered mound over a house built by the ancient Maya that contains the rendering of an ancient figure, possibly the town scribe. The house sits at the edge of the ancient site of Xultún in Guatemala, a city that once housed tens of thousands of people. Excavation and preservation of the site were supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic

  • Three male figures, seated and painted in black. The men, wearing only white loincloths and medallions around their necks and a head dress bearing another medallion and a single feather, were uncovered on the ruined house's west wall. The painting recreates the design and colors of the original Maya mural. Excavation and preservation of the site were supported by the National Geographic Society. Painting by Heather Hurst

  • A Maya king, seated and wearing an elaborate head dress of blue feathers, adorns the north wall of the ruined house discovered at the Maya site of Xultún. An attendant, at right, leans out from behind the king's head dress. The painting by artist Heather Hurst recreates the design and colors of the original Maya artwork at the site. The excavation and preservation of the site were supported by the National Geographic Society. Painting by Heather Hurst

  • A vibrant orange figure, kneeling in front of the king on the ruined house's north wall, is labeled "Younger Brother Obsidian," a curious title seldom seen in Maya text. The man is holding a writing instrument, which may indicate he was a scribe. The painting recreates the design and colors of the figure in the original Maya mural. Excavation and preservation of the site were supported by the National Geographic Society. Painting by Heather Hurst

  • Four long numbers on the north wall of the ruined house relate to the Maya calendar and computations about the moon, sun and possibly Venus and Mars; the dates may stretch some 7,000 years into the future. These are the first calculations Maya archaeologists have found that seem to tabulate all of these cycles in this way. Although they all involve common multiples of key calendrical and astronomical cycles, the exact significance of these particular spans of time is not known. Illustration by William Saturno and David Stuart © 2012 National Geographic

  • The painted figure of a man -- possibly a scribe who once lived in the house built by the ancient Maya -- is illuminated through a doorway to the dwelling, in northeastern Guatemala. The structure represents the first Maya house found to contain artwork on its walls. The research is supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic

  • Conservator Angelyn Bass cleans and stabilizes the surface of a wall of a Maya house that dates to the 9th century A.D. The figure of a man who may have been the town scribe appears on the wall to her left. Excavation and preservation of the site were supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic

  • Never-before-seen artwork -- the first to be found on walls of a Maya house -- adorn the dwelling in the ruined city of Xultún. The figure at left is one of three men on the house's west wall who are painted in black and wear identical costumes. Excavation and preservation of the site were supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic

  • Archaeologist William Saturno of Boston University carefully uncovers art and writings left by the Maya some 1,200 years ago. The art and other symbols on the walls may have been records kept by a scribe, Saturno theorizes. Saturno's excavation and documentation of the house were supported by the National Geographic Society. Photo by Tyrone Turner © 2012 National Geographic