It has recently been suggested by an Italian researcher that the Knight's Tour technique used to decode the "Large Parchment" was copied from an example given by Leonhard Euler from his Paper Solution d’une question curieuse qui ne paroit soumise à aucune analyse ("Solution to a strange problem which does not seem to have been subjected to analysis"), published in 1766.

A summary in English of Euler’s analysis of the Knight’s Tour can be found here: http://www.ktn.freeuk.com/1b.htm

Here is the diagram of the closed solution to the Knight’s Tour that is found in Euler’s Paper:

In 2006 Jean-Luc Chaumeil published his book, Rennes-le-Château – Gisors – Le Testament du Prieuré de Sion (Le Crépuscule d’une Ténébreuse Affaire) that included a chapter reproducing a Paper by Pierre Plantard on a Conference in Rennes-le-Château at the Hôtel de la Tour with Noel Corbu on 17 January 1964 – and whilst this actual "conference" may have been apocryphal – the Conference Paper by Pierre Plantard was later reprinted in issue 3 of Vaincre dated September 1989 (page 19) and was attributed to "Pablo Norberto" .

The article contained a diagram of the Knight’s Tour that was used to decode the "Large Parchment".

Both of the Knight’s Tour techniques given by Euler and Plantard work in relation to decoding the "Large Parchment" correctly – but Plantard’s technique differs from Euler’s in that his technique works in reverse order – it therefore follows that Plantard did not copy the Knight’s Tour technique from Euler’s Paper and got it from elsewhere.

• Leonhard Euler was not the first European to offer a solution to the Knight’s Tour; he was the first to produce a mathematical paper on the problem.