The trial of 29 people accused of involvement in train bombings that killed 191 people in March 2004 has opened in the Spanish capital, Madrid.
Seven suspects, most of whom are Moroccan, face charges of murder and belonging to a terrorist group.
The first defendant, Rabei Osman, said he had nothing to do with the bombings and denied links to Islamic extremists.
The trial is expected to last for several months and hear from hundreds of witnesses and police experts.
More than 1,700 people were injured in the multiple bomb attacks on four rush-hour trains in Madrid.
Investigators in Spain have attributed the attacks to a local cell of Islamic extremists inspired by al-Qaeda.
'No relation to the attacks'
A bullet-proof chamber was set up for 18 of the suspects, packed together on wooden benches. The other 11 sat in the main courtroom - they have been out on bail.
TRIAL IN FIGURES
29 men on trial
Six charged with 191 counts of murder and 1,755 of attempted murder
One is charged with 192 counts of murder and 1,755 of attempted murder
They face up to 40,000 years in jail each
22 others face lesser terror-linked charges
About 600 witnesses and 100 experts will give evidence
The indictment itself is 100,000 pages long
A number of counsellors were also in the court building to offer help to attending survivors and relatives of victims.
The first defendant led to the dock was Rabei Osman Sayed Ahmed, also known as Mohamed The Egyptian.
He refused to answer any questions from prosecutors and said he did not recognize the charges against him, but later agree to take questions from defence lawyers.
"I never had any relation to the events which occurred in Madrid," he told the court, denying he was part of al-Qaeda or any other Islamic extremist group.
"Obviously I condemn these attacks unconditionally and completely," he said.
He is one of six people charged with 191 murders and 1,755 attempted murders.
Hundreds of witnesses
A Spaniard believed to have supplied the explosives is accused of 192 murders - the 191 who died in the bombings and a policeman killed when seven key suspects committed suicide in a raid on a flat three weeks later - and 1,755 attempted murders.
The suspects who died in the flat explosion in April 2004 included the alleged plot mastermind, Tunisian Serhane ben Abdelmajid Fakhet.
Of the defendants on trial who are not charged with murder, 11 are from Morocco, eight from Spain and one each from Algeria, Syria and Lebanon.
They face charges including collaborating with a terrorist group and handling explosives.
Lawyers representing the accused have said that all 29 will deny the charges.
The judges will hear from all the suspects. More than 600 witnesses and 100 police and forensic experts will then testify.
The hearings are expected to last until July, with a verdict expected not earlier than October.
This high-profile trial is being keenly watched by victims of the bombings and the Spanish public.
The legal documents have been digitised and will be projected on to screens during the court sessions, which are being broadcast live on national television, radio and the internet
On Tuesday, Spanish officials raised the country's security alert level from low to medium ahead of the trial and the third anniversary of the attacks on 11 March.
Extra police and soldiers will be stationed at key public areas, and water supply and power plants, while the elevated alert is in place, the interior ministry said.