Italian prosecutors have requested the indictment of 29 riot police for alleged brutality against protesters at the G8 summit in Genoa three years ago.
Prosecutors accuse the officers of inflicting injuries on anti-globalisation activists during a pre-dawn raid on a school.
Police say their action was needed to respond to violent demonstrations.
They are charged with vandalism, robbery and illegal possession of explosives during the 2001 summit.
The defendants, who face up to 15 years in jail if convicted, deny the charges.
As the trial opened a Tuesday, demonstrators outside the courtroom said the real criminals were police.
During the summit a 23-year-old demonstrator was shot dead by a policeman.
The officer was investigated by prosecutors, but the case was thrown out by a judge who ruled that he was acting in self-defence.
It is now up to a judge to decide whether the 29 policemen will stand trial.
About 100,000 anti-globalisation protesters descended on Genoa in July 2001.
Small groups threw stones, bottles and incendiary devices at police. Shops were looted and hundreds of cars wrecked.
The police raid on the Diaz school, where hundreds of protesters were sleeping, became one of the most notorious incidents of the summit.
A number of protesters said they were beaten in their sleep.
Local media showed pictures of blood stained walls, smashed computers and windows.
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