Archaeologists say the tombs of a mysterious city have yielded the first example of the use on children of an ancient art: carving or engraving teeth as a sign of beauty.

Evidence of the engraving was discovered on the teeth of a young boy's skeleton found in the ruins of Montezuma's Balcony, whose civilization was far more advanced than any previously thought to exist in the region.Montezuma's Balcony is 310 miles north of Mexico City outside Ciudad Victoria, capital of northeastern Tamaulipas state. Its name is derived from that of Montezuma, the Aztec king.

Tamaulipas, which spent more than $53,000 on the project, plans to open the site to the public this year.

Two canyons and a mountain surround the remote, 12-acre city. It is reached by a steep, rocky road that veers two miles off the main highway to 86 huge slabs of stone named the "grand stairway."

Only from the top of the stairway can the remains of more than 100 circular structures be seen, each up to 50 feet in diameter, built from stacked and fitted rocks.

More than 100 skeletons have been found there.

The remains of a boy, no older than 5, showed evidence of the carving, called dental mutilation, in his two upper incisors and one lower incisor.