The Prieuré de Sion has never existed except in the imagination of the madman who wrote about it and claimed to be a member. Dan Brown can keep on writing amateurish books about it, it won't make it a historical truth.
I'm talking about his ranks. I'm not an expert on Freemasonry, but among the many ranks of the French freemasonry (based on the Accepted Scottish Rite), I think a few use the word Sion. He was a member of the Grand Orient de France, which would hardly be an ultra-catholic lodge: it has been fighting the french Church more or less since the Revolution and had been labelled as the work of Satan by some Pope in the late 19th.
I also disagree with Napoleon's statement. Of course, french freemasonry became a joke between 1799 and 1870, mostly because the Emperors and Kings who ruled during this era did their best to infiltrate freemasonry with their own men. Cambacérès and Louis Murat became unofficial leaders of the french freemasonry respectively during the 1st and 2nd Empire.
Then, after 1870, freemasonry became a major political force in France (much more than it was in 1789, despite all the religious nutjobs claiming 1789 was the first step of a freemason plot). Most french public characters from the left and centre-left were member of one of the various lodges. The Radical Party and the Grand Orient de France were more or less the same thing. The socialist party was also strongly tied to freemasonry.
Though I don't agree at all with any conspiracy theory, it's pretty much a given that most of the laws on which the french republic is based (laïcité, separation of the church and state, the universal aim to improve Man and Society through education) are the work of 3 or 4 important french lodges.
Overall, claiming there's a vast freemason conspiracy is foolish. Each country has its own freemasonry (french freemasonry is deeply anti-religious, unlike British or American freemasonry). Some freemasons are catholics, some are protestants, some - as pointed out earlier - are jews, muslims, hindus or sikhs. Freemasonry is nowadays in Europe a lobby group with little power and a prestige that is slowly fading after each new scandal. Most of the freemasons I know (which is quite telling of the supposed secretive aspect of the group: many people keep bragging about their membership) are simply too stupid to be plotting to establish a New World Order tm.
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