The Priory of Sion is an alleged secret society devoted to protecting the bloodline of Jesus of Nazareth until the 2nd coming, when Christians believe God's kingdom will be established on Earth. According to the myth that was popularised in the nonfiction book "Holy Blood, Holy Grail" and Dan Brown's novel "The Da Vinci Code," Jesus of Nazareth and Mary Magdalene had children with whom the French Merovingian dynasty of the 5th century intermarried. The origin of the myth dates back to 1956, when Pierre Plantard registered the Priory of Sion as an official organisation with the French government, and established a magazine, Circuit, to promote the group.
The group publicly disbanded in 1957. However, documents that were allegedly uncovered in the Rennes-le-Chateau in southern France were anonymously deposited in the National Library in Paris in the mid-1960s, fuelling the legend surrounding the Priory of Sion. In 1993, Plantard admitted that the documents were forged, and the Priory of Sion was a hoax to help him realise his ambitions for political power. While there is ample evidence to verify the hoax, many still maintain that the Priory of Sion is a real organisation that has existed since the 1st century.
Familiarise yourself with former members. The Priory of Sion, whether real or fabricated, was an exclusive group. The pathway to membership may come from knowing who used to be a part of it. The documents at the National Library in Paris, which can be viewed online at http://www.rlcresearch.com/2007/11/11/les-dossiers-secrets, outline the lineage of the membership of the Priory of Sion. Study these documents to uncover modern day links to the organisation.
Create your own Priory of Sion. Plantard admitted to fabricating his Priory of Sion with a group of friends, and planting information about the organisation in strategic locations to legitimise themselves. It may be easier to create your own Priory of Sion than join an organisation that may never have existed. Gather a group of like-minded people and carry on with the traditions of the Priory of Sion, as outlined in the documents at the National Library of Paris.
Join a web-based discussion forum. A number of websites, web forums and discussion groups are devoted to unravelling the mysteries of the Priory of Sion. It may not be possible to join the Priory of Sion, but a web-based discussion group may be the next best thing.
Join the Freemasons. According to the myth, the Priory of Sion sponsored the formation of the Knights Templar in 1188 to protect the roads for Christian pilgrims travelling to The Holy Land. While the exact nature of the relationship is a subject of controversy, the Knights Templar and the Order of the Freemasons have an intimate history. You may have better chances of joining the Freemasons, who have frequent recruitment drives, instead of the Priory of Sion.