The Shroud of Turin - hailed by some as the only tangible proof of Christ on Earth, dismissed by others as a medieval fake - goes on show this weekend for the first time in 20 years with its mystery as deep as ever.

Some 800,000 people from all over the world have already book-ed to see the yellowing linen cloth, which will be on display starting Sunday in a glass case in Turin's cathedral, or Duomo.It will only be the fourth time this century that the public has had a glimpse of the sheet some Christians believe wrapped the body of Christ after his crucifixion. The last time the Shroud was seen in public was in 1978.

The fragile relic nearly didn't make it for this year's display, timed to coincide with the 100th anniversary of the first photograph that revealed to the world the blood-stained, ghostly image of a bearded man with shoulder-length hair.

Fire ripped through Turin's 15th century Duomo in April last year, and the treasured cloth, furled inside an ornate silver casket, was only saved after a courageous fireman smashed through its protective glass case and spirited it to safety.

The Shroud, bearing as it does the apparent marks of torture and crucifixion that correspond with Gospel accounts, is one of Christianity's most revered relics, but also one of its most baffling and controversial.

Moved by the mystery - not least of how the image came to be visible on the cloth in the first place - more than 3 million people flocked to Turin in 1978, some queuing for seven hours.

But within 10 years, the Shroud's reputation was in ruins.

Scientists in Oxford, Zurich and Tucson, Arizona, conducted carbon-dating tests on carefully snipped samples of the cloth in 1988 in a bid to solve the mystery once and for all.

Their sensational result was that the Shroud dated from between 1260 and 1390 - suggesting it was a medieval fake.

Despite the furor their verdict caused, supporters remain convinced the aged linen sheet is the same cloth that wrapped the dead body of Christ nearly 2,000 years ago in Jerusalem.

Ian Wilson, a Shroud expert, wrote last week that along with Easter, he would now be cautiously celebrating "the resurrection of the Shroud."

"In the past three years new scientific evidence has emerged to show that the radiocarbon scientists might have been seriously wrong in believing that their dating of the Shroud in 1988 was conclusive," he wrote.

"For those who conducted the radiocarbon-dating tests did not know that the Shroud was encrust-ed in barely visible living bacteria," he said.