More than 1 million people showed their support for Catalan independence by joining hands to form a 400-kilometre human chain across the northeastern region of Spain.
The demonstration on the region's annual public holiday aimed to illustrate the strength of local backing for political efforts to break away from Spain. The Catalan regional government estimated 1.6 million people in the region of 7.5 million residents took part in the human chain, many of them with red, yellow and blue pro-independence flags draped around their shoulders.
"Today is a historic day. The Catalan people have reaffirmed their determination to be a free state," said Carme Forcadell, president of the Catalan National Assembly, which organised the human chain.
The protest in Catalonia was peaceful, but a small group of Spanish fascists in Madrid stormed their way into the office of the Catalan government's delegation building in the capital.
Television images showed about 10 men with Spanish fascist flags shouting, pushing people, knocking over furniture and hitting a journalist's TV camera. They yelled "Catalonia is Spain!" and quickly left, but reportedly opened a tear gas container, forcing the 100 or so people gathered there to evacuate.
During Francisco Franco's fascist dictatorship from 1939-1975, the Catalan language was banned in schools, publishing and from public use.
Despite sharing many cultural traits with the rest of Spain, many Catalans claim a deep cultural difference based on their language, which is spoken side-by-side with Spanish in the wealthy region.
Catalonia's regional leader Artur Mas has promised to hold a referendum on independence in 2014, but the Madrid-based government has said that such a vote would be unconstitutional.
Polls indicate that the majority of Catalans agree on holding a referendum, though surveys indicate support among residents for independence is around 50 per cent. It falls to less than that when those questioned are asked whether they would want a separate Catalan state outside the European Union.
The Spanish government's refusal to grant Catalonia similar fiscal powers held by the Basque Country - the other region with a strong separatist movement - combined with the country's double-dip recession have swelled the pro-independence ranks in recent years. Many Catalans feel secession would allow them to pull free of Spain's economic troubles.
"It's becoming clearer that we have nowhere to go with Spain. We want to be free," said Montse Espina, a 44-year-old sales representative holding a pro-independence flag in Barcelona.
Pro-independence supporters raised their arms and chanted "Independence!" during the demonstration. There was a festive mood across the countryside, with church bells ringing out in some towns and villages.
In Barcelona, the human chain passed through the city's main square, around the famous Sagrada Familia cathedral and through the Camp Nou Stadium where the Barcelona soccer team plays.
"The message has been sent," Mas said. "If we are not given a way to channel this widespread patriotic movement, then I think the Spanish state has a serious problem with Catalonia."
Spain's deputy prime minister, Soraya Saenz de Santamaria, said Mas was promoting political divisions.
"The worst thing a politician can do is force people to separate" into two groups, she said.