BARCELONA, Spain — Spanish unionists in Catalonia finally found their voice Sunday, resurrecting Spain’s flag as a symbol of patriotism after decades of it being associated with the Franco dictatorship.

In a defiant challenge to plans by Catalonia’s regional government to unilaterally declare independence, hundreds of thousands of people flooded the streets of Barcelona in a surprising outpouring of Spanish unity.

They chanted “Don’t be fooled, Catalonia is Spain” and called for regional president Carles Puigdemont to go to prison for holding an illegal referendum last week. Some of the demonstrators took to rooftops, including families with children, and leaned over ledges overlooking the streets below to wave giant Spanish flags in a city accustomed to the prevalence of the Catalan pro-independence “estelada.”

Spain’s red-and-yellow flag has long been taboo here in Catalonia and throughout the country because it has been linked to groups supportive of Gen. Francisco Franco’s dictatorship. But on Sunday, a sea of Spanish flags, interspersed with some Catalan and European Union flags, dominated Barcelona’s boulevards.

Barcelona police said 350,000 people participated, while march organizers Societat Civil Catalana said that 930,000 people turned out. The march was peaceful and no major incidents were reported.

Puigdemont has pledged to push ahead for independence and is due to address the regional parliament Tuesday “to report on the current political situation.” In the days after the Oct. 1 referendum, the momentum appeared to be on his side. Pro-independence protests were attracting large numbers and he benefited politically from a violent crackdown by Spanish police during the referendum voting.

But now the tide seems to be turning. Catalonia’s top two banks announced they were relocating their headquarters to other parts of Spain because of financial uncertainty if there is an independence declaration. Other companies are reportedly considering leaving Catalonia to avoid being cast out of the EU and its common market in the case of secession.

Sunday’s mass demonstration by pro-unity Catalans puts further pressure on Puigdemont.