Forty-five Italian police and medical staff have gone on trial accused of brutality against protesters arrested during the G8 summit in Genoa in 2001.
The alleged attacks happened after riots during the summit
The case, which opened at a court in Genoa, was adjourned until November.
The defendants - which include senior officers from Genoa - deny the charges, including unlawful violence.
On Friday, in a related case, 28 officers are due appear in court over a raid at a school which protesters were using as a dormitory at the time.
A small number of protesters gathered outside the court on Wednesday.
One wore a sign around his neck, saying: "Repeatedly hit with a club".
More than 600 witnesses are due to be called during the trial, including the former Italian Interior Minister, Gianfranco Fini, who is now the country's foreign minister.
Dozens of people from the UK, Germany, France and the US who claim they suffered injuries, some life threatening, are expected to be among those giving evidence.
The alleged brutality took place as the G8 summit in the Italian port city came to a close after days of mainly peaceful, mass demonstrations.
A small minority, mainly anarchist groups such as Black Bloc, were blamed for the violence and vandalism that broke out.
One protester, Carlo Giuliani, was killed in the subsequent clashes with police.
On the night the protests ended, riot police smashed their way into Diaz school, where many of the demonstrators had been staying.
They reportedly kicked and beat those they found inside. More than 1,000 people were injured; three were left in a coma.
Mark Covell, from London, was one of those who found himself in the front line.
"Three hundred police raided two buildings," he said.
"Within the space of about 15 minutes I was almost killed and there were 92 other protesters, most of which were injured quite badly."
Wednesday's trial concerned the treatment of those who were arrested and taken to a detention camp at Bolzaneto, 6km (4 miles) outside Genoa.
Here they were allegedly beaten again, sprayed with asphyxiating gas and forced to sing pro-Fascist songs.
Some of the most senior officers in the camp, and in the city, are facing trial on charges including abuse of authority and unlawful violence.
But even if the defendants are found guilty, they may escape punishment because of a new law passing through parliament.
Critics say the law has been devised to enable Prime Minister Silvio Berlusconi's former lawyer to escape a jail term on bribery charges, but will also apply to a whole range of criminal offences.