They lurked in the woods, 50 strong, wearing black hoods and bandannas, and wielding tree limbs. At a signal given by one of their number, they sprang forward and threw their debris across a road here, creating a barricade that brought traffic to a screeching halt.
That little insurgency, and dozens like it, kept tensions high on the first day of the Group of Eight meeting in northern Germany.
Several thousand protesters clashed with riot police, who used tear gas and water cannons to disperse crowds that blocked roads and railways leading to the site of the meeting, the Baltic Sea resort of Heiligendamm.
Eight police officers were injured, and 15 demonstrators were detained, a police spokesman, Luedger Behrens, told Reuters. He said the police used force after being pelted with stones.
While the protests had little effect on the leaders — who were flown by helicopter from Rostock, the nearest major city, to Heiligendamm — the protestors did manage to foil some of the elaborate security precautions for the summit.
The police had erected a 7.5-mile-long fence, completely cutting off the resort, and had banned any protests within 200 yards of the fence. By midday, though, an estimated 10,000 demonstrators — many wearing clown makeup and tinted hair — had penetrated the restricted zone and massed at the fence.
Evading checkpoints by crossing through oat fields, protesters also blocked main roads leading from the Rostock airport to the summit site. After numerous standoffs, some lasting several hours, riot police clad in helmets waded into the crowd, occasionally swinging truncheons.
Organizers of the protest complained that the police response was heavy-handed, perhaps because a demonstration on Saturday in Rostock turned violent and resulted in at least 400 police injuries.
"It's not just the demonstrators who are being aggressive," said Monty Schaedel, a local organizer of the protests. "It's the police, who are escalating the trouble with their own aggression."
Schaedel expressed regret for the violence in Rostock. The majority of anti-globalization protesters, he said, were peaceful. They come from a wide array of social activist groups, including Attac, Greenpeace, Friends of the Earth, and the Global Call to Action Against Poverty.
But a minority — often those who wear the black hoods — is determined to disrupt the meeting, which they regard as illegitimate. At one point, the protests forced the police to close all the entrances to Heiligendamm.
"I'm here because this so-called democratic meeting is not democratic," said Lars, a 27-year-old German who declined to give his last name. "I didn't want to just sit and do nothing about it."
As a phalanx of riot police advanced toward Lars, he and his friends decided to retreat. Earlier, they said, they had been in a clash in which several demonstrators were roughed up. In a nearby area, three protestors sat under the gaze of police, their hands cuffed behind their backs with plastic bands.
German authorities expected trouble at this meeting, which has become an annual flashpoint for anti-globalization groups.