More than 100,000 people have demonstrated in Bilbao on behalf of jailed members of the underground Basque separatist organisation ETA and for independence of the region from Spain.
Participants marched peacefully through the city centre on Saturday demanding freedom for more than 600 ETA prisoners.
Police said about 110,000 people were in the streets.
They repeatedly called out "Amnesty for all" and "Freedom, freedom". Many people also cried out independence slogans.
The demonstration was planned for Friday, but authorities would not allow it.
The ruling nationalist party and a socialist organisation then called a new protest for Saturday.
ETA began a campaign of violence against the Spanish government in 1968. Its goal was independence for the Basque region in northern Spain.
The group renounced violence in 2011. The Spanish government has nonetheless refused to negotiate with the group, calling on it to disband completely.