Throngs of demonstrators filled Barcelona's streets in a regional independence protest fueled by Spain's economic crisis.
September 11 is known as Catalonia's national day, and for years there have been demonstrations pushing for independence in the northeastern region.
But Tuesday's turnout was larger than expected, Spanish newspapers reported.
Hours before, Artur Mas, the president of Catalonia's regional government, attended official ceremonies commemorating the day. Later, he issued a warning: if Spain's central government in Madrid doesn't give the region more control over its tax dollars, independence could be an option.
"If we do not reach a financial agreement with the central government, the path to freedom for Catalonia is open," he said.
Many Catalans complain that Catalonia provides many riches and taxes to the rest of Spain -- more than they owe.
Changing this structure and creating a new "fiscal pact" is a primary goal of Mas' government.
"If you compare the money we send to Madrid every year and the money we get back from Madrid, there is a difference -- a near difference of $20 billion," Mas told CNN in June.
In Madrid, Spanish President Mariano Rajoy has said that what the country needs aren't independence protests, but unity and strength to come out of the economic crisis.
Some analysts say Spain's financial problems have pushed Catalonia to ask for more, now.