The Knights Templar were disbanded in the 14th Century

The book is based on a document known as the Chinon parchment, found in the Vatican Secret Archives six years ago after years of being incorrectly filed.

The document is a record of the heresy hearings of the Templars before Pope Clement V in the 14th Century.

The official who found the paper says it exonerates the knights entirely.

Prof Barbara Frale, who stumbled across the parchment by mistake, says that it lays bare the rituals and ceremonies over which the Templars were accused of heresy.

In the hearings before Clement V, the knights reportedly admitted spitting on the cross, denying Jesus and kissing the lower back of the man proposing them during initiation ceremonies.

The Pope was obliged to ask for pardons from the knights - the document absolves them

Prof Barbara Frale

Vatican Secret Archives official

However, many of the confessions were obtained under torture and knights later recanted or tried to claim that their initiation ceremony merely mimicked the humiliation the knights would suffer if they fell into the hands of the Muslim leader Saladin.

The leader of the order, Jacques de Molay, was one of those who confessed to heresy, but later recanted.

He was burned at the stake in Paris in 1314, the same year that the Pope dissolved the order.

However, according to Prof Frale, study of the document shows that the knights were not heretics as had been believed for 700 years.

In fact she says "the Pope was obliged to ask for pardons from the knights... the document we have found absolves them".

Details of the parchment will be published as part of Processus contra Templarios, a book that will be released by the Vatican's Secret Archive on 25 October.