The former French Prime Minister, Dominique de Villepin, has gone on trial charged with plotting to discredit President Nicolas Sarkozy.
It is alleged that Mr de Villepin tried to manipulate a judicial investigation to hurt Mr Sarkozy's chances of winning the 2007 presidential election.
If found guilty, Mr de Villepin could face up to five years in jail and a 45,000 euro (£41,000) fine.
The former prime minister denies any wrongdoing.
"I am here because of one man's will. I am here because of the dogged determination of one man, Nicolas Sarkozy, who is also president of the French republic," he told journalists before entering the courtroom.
Hugh Schofield BBC News, Paris
The languid figure of Dominique de Villepin arrived at the court surrounded by well-wishers and gave a characteristically eloquent statement of what will amount to his defence.
His was a political trial, he said, and one taking place thanks to the obsession of one man - President Nicolas Sarkozy.
The two men once shared government together but to describe them as political rivals would be something of an understatement.
Their mutual hatred has long seethed behind the scenes, and now this unprecedented court case has brought it to the surface.
"I will come out of this a free man and exonerated," said Mr de Villepin, dressed in a dark suit and tie, looking tanned and relaxed.
"I know that truth will prevail."
"The trial of the decade" - as it has already been labelled by some French media - is likely to last about four weeks, although its verdict is not expected until much later.
It is being held in the Grande Chambre of the Palais de Justice next to Notre Dame cathedral - the same Paris courtroom where Queen Marie Antoinette was sentenced to the guillotine in 1793 by France's revolutionary tribunal.
Witnesses are due to include another former prime minister, Jean Pierre Raffarin, and a smattering of past and present intelligence chiefs. Although he is a plaintiff in the trial Mr Sarkozy, as president, will not have to testify.
Mr de Villepin's lawyers have asked the court to strip Mr Sarkozy of his status as a civil plaintiff to end what they say is his distorting influence over the case.
"We want to be tried through a fair procedure," said Henri Leclerc, for the defence.
Representing the president, who was not present, Thierry Herzog argued his client's legal action pre-dated the charges against Mr de Villepin and merely reflected Mr Sarkozy's desire to know the truth about the fake listing.
Mr de Villepin stands accused of "complicity in false accusation, complicity in using forgeries, receipt of stolen property and breach of trust" and is expected to testify next week.
The case dates back five years, when Nicolas Sarkozy's name appeared on a list of top politicians and businessmen sent to Mr de Villepin.
It was alleged those named on the list had received bribes from international arms sales.
THE CLEARSTREAM ACCUSED
Dominique de Villepin: Former PM, 55, denies accusations he tried to circulate details of Sarkozy's illegal bank accounts, even though he knew they were fake
Jean-Louis Gergorin: Former Airbus VP, 63, accused of faking Clearstream bank accounts as part of Airbus power-struggle, says he accepted accounts in good faith
Imad Lahoud: Computer expert, 42, says he faked Clearstream accounts on Gergorin's behalf, introducing Sarkozy's name on Villepin's instructions
Florian Bourges: Accountant, 31, accused of stealing Clearstream documents and breach of trust
Denis Robert: Journalist and author, 41, who broke the story, accused of dealing in stolen property and breach of trust
Part of the intention of drawing up the elaborate forgery seems to have been to discredit senior figures in the aerospace group EADS, to influence the outcome of a boardroom leadership struggle, says the BBC's Emma Jane Kirby in Paris.
In 2006 the former vice-president of EADS Jean Louis Gergorin admitted that he gave the list, which also included his boss Philippe Delmas, to judicial authorities - but he also claims he was acting on orders from Mr de Villepin and President Chirac.
When a judge concluded the listings were false, the focus of the investigation quickly became who was behind the spurious allegations, says our correspondent.
Magistrates want to know whether that person was Mr de Villepin, and whether he attempted to conduct a smear campaign against Mr Sarkozy to spoil his chances of winning the presidential election.
Mr de Villepin was questioned over the so-called "Clearstream affair" in December 2006 and has been under investigation since 2007.
The name Clearstream comes from the Luxembourg bank where the individuals on the list - including Mr Sarkozy - were supposed to be account holders.
Mr de Villepin and Mr Sarkozy were both ministers under President Jacques Chirac, but were intense rivals.
Mr de Villepin was preferred by Mr Chirac, but it was Mr Sarkozy who won party support to succeed the president.
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