The defendants, who have all pleaded innocent, are nine men of Pakistani nationality or origin, and two from India.
Vicente Gonzalez Mota, a prosecutor, said the attack was allegedly planned because of Spanish troops being stationed in Afghanistan.
'Operational capability'
From the outset there have been doubts as to how close the men were actually to staging what would have been Spain's first suicide terrorist attack.
In a charge sheet released several weeks ago, Gonzalez Mota's only mention of explosives was to say police who made some of the arrests seized 18 grammes - less than an ounce - of white powder that came from emptying out fireworks.
He said police also found timers, steel balls and air-gun pellets to serve as shrapnel, and other material for making bombs.
When indictments were handed down in June of this year, Ismael Moreno, the investigating magistrate, wrote that the cell had achieved "operational capability" in terms of manpower and "was apparently very close to achieving full technical capability in terms of explosive devices".
However, he said the amount of explosives found was enough for training purposes but not to stage a major attack.
Perhaps because of this lack of firepower, the cell is not accused of actually conspiring to stage a terrorist attack but rather of belonging to a terrorist organisation.
The cell acted under the inspiration of Tehrik-e-Taliban Pakistan, the Pakistani Taliban movement, led at the time by Baitullah Mehsud, and plans for the Barcelona attack were later claimed in a video by Maulvi Omar, a spokesman for the group, Gonzalez Mota wrote.