Around 350,000 people rallied in Barcelona, turning the streets into a sea of independence flags in the latest mass protest against Spain's jailing of nine separatist leaders.
The turnout figure was given by the local police as vast crowds packed into a wide avenue running between the waterfront and the city's towering Sagrada Familia basilica, which was once again closed to visitors.
Catalonia has been gripped by unrest since the 14 October Supreme Court verdict which unleashed a wave of huge demonstrations that quickly turned violent, with angry protesters hurling rocks and Molotov cocktails at riot police, who hit back with tear gas, foam rounds and rubber bullets.
The crisis began two years ago when the region staged a banned referendum on 1 October that was marred by police violence, then issued a short-lived declaration of independence, triggering Spain's worst political crisis in decades.
Today's rally was called by the ANC and Omnium Cultural, the region's two biggest grassroots pro-independence groups that have organised some of the largest separatist protests in recent years.
Marching down the spacious boulevard, demonstrators held up banners reading "We won't give in" and chanting "1 October, we won't forgive, we won't forget".
As a police helicopter flew overhead, they broke into loud boos and whistling, an AFP correspondent said.
"I feel really angry," said a 26-year-old computer technician from Tarragona called Marc, who did not give his surname and described the heavy prison sentences handed to nine separatist leaders as "totally over the top, inhuman, and shameful".
"The violence doesn't sit well with me but it's normal to have a bit of upheaval like we've seen in Chile and Ecuador," he said of a wave of mass protests in Latin America.
"There are different ways of protesting but we have one objective: independence."
Catalans remain sharply divided over the question of separating from Spain, with a September poll showing 44% in favour but 48.3% against. The violent protests over the verdict have only deepened that division.
The violence eased off last week although the protests continued, with thousands of flag-waving students marching peacefully through the city yesterday evening.
More than 600 people have been injured so far in the protests, among them 367 civilians, four of whom lost an eye, Catalan health officials say, with government figures showing 289 police were also hurt.
Earlier, thousands rallied in Madrid in defence of Spain's unity at a demonstration called by the far-right Vox party, which has taken a very tough line on Catalan separatism and wants all regional pro-independence parties banned.
Although the faction only entered parliament in April, polls indicate it might become the third-largest party following the 10 November election.
Tomorrow, activists from Catalan Civil Society (SCC) will hold a counter-demonstration by those who want the region to remain part of Spain and who want the protest violence to end.
"Those who oppose independence are a majority, and that is an important message for Catalonia, for Spain and the world, where often separatism is associated with Catalonia," SCC head Fernando Sanchez Costa told AFP.
"It's important to go back out and say: that's enough violence and confrontation," he said, warning that the unrest was causing a lot of damage to Catalan society.
Until now, the Socialist government of Pedro Sanchez has turned a deaf ear to repeated calls for dialogue from regional president Quim Torra, who wants to secure Madrid's agreement for a referendum on independence.
"What we will not talk about is the right to self-determination," Carmen Calvo, Sanchez's deputy, told journalists on Saturday.
"If, as president Torra has said every day, the aim is to break up Spain's territorial unity and separate Catalonia from Spain, we simply cannot talk," she said.
"Unilaterally breaking the rules of the game is not an option."