King Juan Carlos and government officials observed three minutes of silence at a solemn ceremony in memory of the 191 people killed and more than 1,800 wounded in the attacks of March 11, 2004.
Twenty-nine people, mostly Islamic militants, are currently on trial in Madrid over the attacks.
The memorial includes a tower of 15,000 glass bricks that catches light and channels it into an underground chamber near where explosions ripped through four trains at rush hour.
The architects said light was a key element of their project.
(AP, Reuters)
