They came armed with iron bars and hammers, carrying bottles, stones and metal pe-tanque (bowling) balls to throw at French gendarmes and riot police. Some wore ski masks or carnival disguises and waved Basque and Corsican flags.
They charged the barricade on the Rue de la Republique shortly after dawn, within sight of the ugly glass and concrete Acropolis convention centre where the leaders were about to meet.
The French EU Presidency hoped the morning assembly of 12 candidate countries with 15 member-states would be historic. But the politicians appeared under siege.
Police fired so much tear gas that some of the delegates arriving at 9 a.m. were seized with fits of coughing. When the battle subsided, seven of the rioters were in jail and 21 policemen were injured.
The rioters, widely and misleadingly called "anti-globalisation protesters", set fire to the Banque Nationale de Paris and sacked an estate agent's office. "Down with money", "Capitalism kills; let's destroy it!" and "F . . . the police" said the graffiti they left behind them. A British Socialist Worker poster lay on the pavement. "Whose Europe?" it said. "Our Europe. Whose world? Our world. Join the resistance".
In the streets around the Acropolis, shopkeepers and gendarmes braced themselves for the return of the protesters.
Within the European Council, the battle of wills was just starting. At their press conference, President Jacques Chirac, who as head of the French Presidency stands to win or lose most at the summit, the Commission President, Mr Romano Prodi, and the French Prime Minister, Mr Lionel Jospin, all condemned the violence that marred the opening of the summit.
Mr Chirac stands accused by the left-wing press, and some French civil servants, of using France's EU Presidency to "destabilise" Mr Jospin.
His June speech in the Bundestag on the future of Europe and his recent upstaging of Mr Jospin in the fight against BSE were the two most flagrant examples. The Prime Minister has refused to be drawn, saying he will talk about Europe in January, once the Presidency is over.
A French journalist asked about widespread reports that the two men's "cohabitation" has poisoned and paralysed the French Presidency, about repeated allusions to French "arrogance".
"My dear Veronique", Mr Chirac responded, "you should never believe anything that is said or written."
A former commissioner for competition, Mr Karel van Miert, from Belgium, told Le Monde that the French Presidency had been very disappointing. On all issues, he added: "The French only defended their own interests". Yet Mr Jospin knew of no European head of state or government saying such rude things. "The French Presidency has done its work", he stated.
Such criticism dismays the French diplomats who prepared the Nice summit. Trying to get agreement on the reform of European institutions was "like climbing the north face of Mount Everest", said Mr Bernard Valero, a spokesman for the Foreign Ministry. "The negotiations are especially difficult because they are about power", he explained.
The focus on the Inter-Governmental Conference made France's European partners lose sight of the achievements of the French Presidency, Mr Valero added.