The French authorities said Saturday that 10,000 protesters had assembled on the French side of the frontier and 7,000 on the German side. Protest organizers said the total was about 30,000.  According to the French police, 1,000 violent agitators attacked security forces, leaving 12 protesters lightly injured. There was no information on the number of arrests, though there were many.  Reiner Braun, one of the protest organizers, said that a peaceful demonstration had been hijacked by a small group of anarchist troublemakers, known as the Black Bloc, but he also condemned the police tactics.  “I do not accept the behavior of the Black Bloc,” Mr. Braun said. “But it was pure provocation from the police. They and the Black Bloc are like brother and sister; they need each other.”  Before the arrival of world leaders, France deployed up to 10,000 police officers and gendarmes. Strasbourg, a charming city of narrow streets and a soaring cathedral, was nearly emptied of ordinary life as entry into the city’s center was barred to nonresidents without summit meeting credentials.  Stores and restaurants, at least those that remained open, were nearly empty, bringing numerous complaints from owners.  Maison Kammerzell, a famous restaurant by the cathedral, was closed Friday afternoon because President Nicolas Sarkozy of France wanted a private lunch with his wife. But running late, the Sarkozys canceled, leaving the restaurant, which has 360 seats, with no customers. Given the security measures, it was practically empty again Friday night except for police officers wanting to use the bathrooms.  The economic downturn appears to have reinvigorated European protest movements. A mixture of antiglobalization campaigners and peace protesters came together in opposition to the NATO summit meeting.  Mark Krantz, an antiwar activist from Manchester, England, said that the economic recession had sharpened support for protest politics. “Our message is jobs, not bombs, and welfare not warfare,” he said, adding, “The era of protest has returned.”  Around midday Saturday, several thousand protesters, moving toward the Bridge of Europe, found their way barred by lines of riot police officer who fired dozens of tear gas canisters. Demonstrators hurled cobblestones at the police before the police pulled back, allowing the demonstrators through.  When the protesters moved on to the bridge, they found that the German riot police had blocked demonstrators from the other side from crossing the bridge to join them. The protesters erected makeshift barricades and set the border post on fire. Then black-clad protesters smashed their way into the Ibis Hotel, setting it on fire.  Protesters blamed police tactics for provoking the demonstrators, some suggesting that they were deliberate attempts to discredit the event.  “We came to the bridge and it was blocked by the police,” said Clemens Leder, 23, a politics and law student from Görlitz, Germany. “I think it was in the interest of the police to cause trouble because they have to show that they are right to attack.”  Mr. Braun, an organizer, said that the protest could not be judged a success. “We wanted to demonstrate peacefully,” he said.  A version of this article appears in print on , on Page A14 of the New York edition with the headline: Riots Erupt Near Bridge That Links 2 Countries. Order Reprints| Today's Paper|Subscribe
NATO’s summit meeting was supposed to symbolize the unity of Europe, but the celebration was marred by rioting near a bridge that spans the border between Germany and France.