Wearing yellow ribbons on their lapels to signify support, they filled the length of the Avenue Marina that runs from the beach to Barcelona's iconic Sagrada Familia church, while the jailed leaders' families made speeches.
Catalonia's two main grassroots independence groups called the march, under the slogan "Freedom for the political prisoners", after their leaders were remanded in custody on charges of sedition last month.
Barcelona's police said that 750,000 people attended the rally. The protest is seen as a test of how the independence movement's support has fared since the Catalan government declared independence on 27 October, prompting Spanish Prime Minister Mariano Rajoy to fire its members, dissolve the regional parliament and call new elections for December.
Libertas! Libertat! Liberdad! Liberdade! Liberty! Persons of Nation of Catalonia have the right of freedom of choice them own future by democratic and consensual ways... force can´t block the trend to a deep autonomy as "Region", a State in a federation or an independent State...