Catalans gathered in five cities across the northeastern region on Sunday, including Barcelona, and waved yellow banners in time to music, symbolizing the rhythm of a beating heart uniting an independent republic.
Police said that in Barcelona alone about 540,000 people took part. The mass rally on Catalonia's national day, La Diada, comes as the pro-independence local assembly vows to press ahead with plans to form a new state in 2017, raising pressure on leaders in Madrid to respond at a time of disarray in national politics.
The long-simmering separatist movement, in a region that produces about a fifth of Spain's economic output, erupted in 2012 during a deep economic crisis and a stand-off with Madrid over demands for more autonomy, according to Reuters.
Catalonia, home to 7.5 million people, has its own language and distinct culture, as well as a long-standing industrial tradition and a thriving tourism sector.