Who are the Sènèchaux and the master of the Priory of Sion in The Da Vinci Code by Dan Brown?
Jacques Saunière, an author and curator at the Louvre, is the Grand Master of Priory of Sion. He is murdered right before the novel opens. As Grand Master, he knows important secrets about the Holy Grail, such as its location. He remains an important presence in the novel despite being dead, because he leaves a trail of clues for Langdon to follow. The list of past Grand Masters of the priory show they have all been important people and include Leonardo da Vinci.
The Senechaux are the three men in the Priory of Sion who rank just below the Grand Master and are a part of his inner circle. They too know the location of the Holy Grail. They are trained to lie about what they know to keep the secrets of the grail safe. They are being murdered in the novel by Silas, who works for Opus Dei.
In The DaVinci Code, the Senechaux and the Grand Master of the Priory of Sion are the men who are put in charge of keeping the Holy Grail safe. At the time of the novel, Jacques Sauniere, Sophie Neveu's grandfather, is the Grand Master, but he is murdered just before the book opens. As Langdon and Sophie try to solve his murder, they figure out the clues that reveal details about the Priory and the Senechaux. At one point in the novel, there is a list of all the past Grand Masters, and some famous historical names appear listed here. During the course of the book, it is unclear who will take over Jacques's role now that he is dead--the other men in his circle were also murdered.