For 600 years, a bundle of charred, stained, straw-colored linen has been Christendom's most controversial holy relic - a burial shroud that many believe bears the true image of Jesus Christ imprinted at the instant of resurrection.
In 1978, more than 30 American scientists in the Shroud of Turin Research Project (STURP) photographed it, probed it with infrared thermography and X-rays, and conducted 1,000 chemical tests on shroud fibers to determine the nature of the image.
Scientific tests have only multiplied its mysteries.
But scores of experiments also have proved what the shroud isn't.
It has been alternately venerated and dismissed as a cruel fraud.
The shroud has prompted more than 275 books and, in Atlanta, even a tourist attraction arranged around photographs of its mysterious image.
The Roman Catholic Church has never taken an official position on its authenticity.
At its simplest level, the shroud is a length of antique cloth with a herringbone weave, measuring 14 feet long and 3 feet wide.
It has been damaged by fire, soaked in water, and folded so often it has permanent creases.
On its surface is the faint, life-sized image of a bearded man who appears to have been beaten, whipped and crucified.
Dark splotches at the man's wrists, ankles and forehead have been identified tentatively by forensic tests as human bloodstains.
Despite almost a decade of intense scientific scrutiny, researchers still haven't wrung the truth from the 14-foot shroud.