The mysteries of the Order of the Knights Templar could soon be laid bare after the Vatican announced the release of a crucial document which has not been seen for almost 700 years.

A new book, Processus contra Templarios, will be published by the Vatican's Secret Archive on Oct 25, and promises to restore the reputation of the Templars, whose leaders were burned as heretics when the order was dissolved in 1314.

The Knights Templar were a powerful and secretive group of warrior monks during the Middle Ages. Their secrecy has given birth to endless legends, including one that they guard the Holy Grail.

Recently, they have been featured in films including The Da Vinci Code and Indiana Jones and the Last Crusade.