Medieval knights hid and secretly venerated The Holy Shroud of Turin for more than 100 years after the Crusades, the Vatican said yesterday in an announcement that appeared to solve the mystery of the relic’s missing years.

The Knights Templar, an order which was suppressed and disbanded for alleged heresy, took care of the linen cloth, which bears the image of a man with a beard, long hair and the wounds of crucifixion, according to Vatican researchers.

The Shroud, which is kept in the royal chapel of Turin Cathedral, has long been revered as the shroud in which Jesus was buried, although the image only appeared clearly in 1898 when a photographer developed a negative.

Barbara Frale, a researcher in the Vatican Secret Archives, said the Shroud had disappeared in the sack of Constantinople in 1204 during the Fourth Crusade, and did not surface again until the middle of the fourteenth century. Writing in L'Osservatore Romano, the Vatican newspaper, Dr Frale said its fate in those years had always puzzled historians.

However her study of the trial of the Knights Templar had brought to light a document in which Arnaut Sabbatier, a young Frenchman who entered the order in 1287, testified that as part of his initiation he was taken to “a secret place to which only the brothers of the Temple had access”. There he was shown “a long linen cloth on which was impressed the figure of a man” and instructed to venerate the image by kissing its feet three times.

Dr Frale said that among other alleged offences such as sodomy, the Knights Templar had been accused of worshipping idols, in particular a “bearded figure”. In reality however the object they had secretly venerated was the Shroud.

They had rescued it to ensure that it did not fall into the hands of heretical groups such as the Cathars, who claimed that Christ did not have a true human body, only the appearance of a man, and could therefore not have died on the Cross and been resurrected. She said her discovery vindicated a theory first put forward by the British historian Ian Wilson in 1978.

The Knights Templar were founded at the time of the First Crusade in the eleventh century to protect Christians making the pilgrimage to Jerusalem. The Order was endorsed by the Pope, but when Acre fell in 1291 and the Crusaders lost their hold on the Holy Land their support faded, amid growing envy of their fortune in property and banking.

Rumours about the order’s corrupt and arcane secret ceremonies claimed that novices had to deny Christ three times, spit on the cross, strip naked and kiss their superior on the buttocks, navel, and lips and submit to sodomy. King Philip IV of France, who coveted the order’s wealth and owed it money, arrested its leaders and put pressure on Pope Clement V to dissolve it.

Several knights, including the Grand Master, Jacques de Molay, were burned at the stake. Legends of the Templars’ secret rituals and lost treasures have long fascinated conspiracy theorists, and figure in The Da Vinci Code, which repeated the theory that the knights were entrusted with the Holy Grail.

In 2003 Dr Frale, the Vatican’s medieval specialist, unearthed the record of the trial of the Templars, also known as the Chinon Parchment, after realising that it had been wrongly catalogued. The parchment showed that Pope Clement V had accepted the Templars were guilty of “grave sins”, such as corruption and sexual immorality, but not of heresy.

Their initiation ceremony involved spitting on the Cross, but this was to brace them for having to do so if captured by Muslim forces, Dr Frale said. Last year she published for the first time the prayer the Knights Templar composed when “unjustly imprisoned”, in which they appealed to the Virgin Mary to persuade "our enemies” to abandon calumnies and lies and revert to truth and charity.

Radiocarbon dating tests on the Turin Shroud in 1988 indicated that it was a medieval fake. However this had been challenged on the grounds that the dated sample was taken from an area of the shroud mended after a fire in the Middle Ages and not a part of the original cloth.

After the sack of Constantinople it was next seen at Lirey in France in 1353, when it was displayed in a local church by descendants of Geoffroy de Charney, a Templar Knight burned at the stake with Jacques de Molay.

It was moved to various European cities until it was acquired by the Savoy dynasty in Turin in the sixteenth century. Holy See property since 1983, the Shroud was last publicly exhibited in 2000, and is due to go on show again next year.

The Vatican has not declared whether it is genuine or a forgery, leaving it to believers to decide. The late John Paul II said it was “an icon of the suffering of the innocent in every age.” The self proclaimed heirs of the Knights Templar have asked the Vatican to “restore the reputation” of the disgraced order and acknowledge that assets worth some £80 million were confiscated.

The Association of the Sovereign Order of the Temple of Christ, based in Spain, said that when the order was dissolved by Pope Clement V in 1307, more than 9,000 properties, farms and commercial ventures belonging to knights were seized by the Church. A British branch also claiming descent from the Knights Templar and based in Hertfordshire has called for a papal apology for the persecution of the order.