PALENQUE, Chiapas — There is a legend that the ancient Maya possessed 13 crystal skulls which, when united, hold the power of saving the Earth — a tale so strange and fantastic that it inspired the latest Indiana Jones movie.

Experts dismiss the hundreds of existing crystal skulls as fakes that were probably made by colorful antiquities traders in the 19th century. But Mayan priests worship the skulls, even today, and real-life skull hunters still search for them.

The true story of the skulls stretches over continents and hundreds of years, and may be even more extraordinary than the tale portrayed in this fourth installment of the Harrison Ford franchise.

It's unclear what version of the tale will appear in "Indiana Jones and the Kingdom of the Crystal Skulls," which opens in U.S. theaters on May 22. The plot apparently revolves around a race against the Soviets to find the skulls.

Distributor Paramount Pictures refused requests for interviews or information on the film, the first Indiana Jones movie since "The Last Crusade" came out in 1989.

Few of today's crystal skulls can be documented any further back than the 1860s, when Europe was swept by a rage for pre-Hispanic "relics." Frenchman Eugene Boban, a colorful antiquities dealer with a checkered past and murky political ties, set up a store here to supply the trade after the French invaded Mexico. Eventually he carted skulls around between New York, Paris and Mexico City, selling them to private collectors.

Buyers were often told that the skulls were made by the Mayas, whose civilization peaked between 300 and 900 A.D. But no crystal skull has ever been excavated from a documented archaeological site.

Some believe the skulls can emit and focus light, project visions and even influence terrestrial forces. Today, these beliefs persist in the jungles of southern Mexico among the Lacandon, the last unassimilated Mayans, some of whom still worship the skulls.

In the shadow of the Palenque ruins, Lacandon priest K'in Garcia fans copal incense and holds a heavy crystal skull above his head during ceremonies for Hacha'kyum, the Mayan god of creation.

Garcia, son of the Lancandon's most respected elder, Chan Kin, believes the skull has special powers, including the ability to stave off sickness and deforestation in the rain forest where the last Lacandon still live.

"When I am alone at night, at about 2 a.m., it starts to glow, it emits light, and it stays like that for about a minute," Garcia said.

Garcia says the skull was given to him by a local man — and while he believes it is very old, he doesn't know where it came from.

Thousands of miles away in Washington, Jane MacLaren Walsh keeps one of the skulls in her office at the Smithsonian Institution. She doubts the ancient Mayans ever had any such skulls.