Spain has been marking the second anniversary of the Madrid train bombings, in which 191 people died.
The 10 bombs were the country's worst terrorist attack
The prime minister attended a sombre wreath-laying ceremony in the Forest of Remembrance at noon, which was followed by a five-minute silence.
A delegation from Morocco - the country of origin of many of the suspects - took part in some of the events.
Investigators believe Islamic militants linked to cells elsewhere in Europe attacked the four commuter trains.
A number of key suspects killed themselves in a stand-off with police weeks after the bombings, but the investigation to find others involved has continued.
Twenty-five people are being held in jail pending trial. The investigation into the attacks is expected to be concluded soon.
Prime Minister Jose Luis Rodriguez Zapatero led tributes to the victims at the memorial garden, where 191 olive and cypress trees are planted in memory of the dead.
Two schoolchildren, an Algerian girl and a Spanish boy, laid a wreath to open the commemoration ceremony.
Earlier in the day, a Moroccan delegation observed a few minutes of silence, lit candles and placed flowers at Atocha train station, which was targeted in the massacre.
The Moroccan Caravan for Peace and Solidarity set out in buses on 5 March, stopping in several Spanish cities.
"We want to express our solidarity and support for the Spanish people and show that the Moroccan people are one of peace and against terrorism," member Mohamed Boujida said.
Meanwhile Spaniards gathered at Madrid's central square, the Puerta del Sol, to join a morning wreath-laying ceremony.
"I feel like I should be present here. It's a date for reflection and that fills me with sadness as well. I'm here as part of Madrid. After those attacks I see life very differently," student Ignacio Valera told the BBC.
"We must work together in the world to make sure this doesn't happen again in any part of the world," added Maria Frances Carmedida.
The 10 co-ordinated blasts on the morning of 11 March 2004 were the country's worst terrorist attack.
The explosions came three days before a general election, in which the Socialists ousted the right-wing Popular Party (PP) of then Prime Minister Jose Maria Aznar.
The government initially blamed armed Basque separatists Eta for the attacks, an error which is widely believed to have contributed to the Popular Party's unexpected defeat.
Correspondents say Spanish victims' associations were keeping a low profile, as they did 12 months ago.
In 2005 the Association of Madrid Bombing Victims said it would boycott all the events, protesting that the pain of victims and relatives had been used as a political football.