As music blared from giant speakers -- from British band Coldplay to Spanish singer Manolo Escobar's "Y viva Espana" ("And long live Spain" in Spanish) -- pro-unity protesters banded together on the square.
Unhappy with Catalonia's secession bid, many also directed anger at Prime Minister Mariano Rajoy, whom they accuse of having been too soft on the region's separatist leaders.
"It is a disgrace what happened in Catalonia, and it's a disgrace what happened after," said Carlos Fernandez, a 41-year-old mining engineer.
On Friday, the Catalan parliament declared unilateral independence.
Rajoy replied by axing Puigdemont and his executive, dissolving parliament, and calling snap December 21 regional elections to quash what he termed an "escalation of disobedience."
"Nothing is going to change in two months," said Fernandez of Rajoy's intervention, "it's just prolonging the problem."
Sitting on a concrete ledge clutching a large red and yellow national flag, he said he was disappointed at the low pro-unity turnout.
"It's because of what the government said yesterday, many people think that it's all solved," he said.
Speeches began at midday.
"Today, we have all come to demonstrate our unity, to proclaim that we will get Catalonia back," one presenter told the crowd.
To cheers and shouts of "prison for Puigdemont," she added: "We won't stop until we see them in jail."
Spanish prosecutors have announced they will next week file charges of "rebellion" against Puigdemont -- a crime punishable by up to 30 years in prison.
Near the square, a large banner proclaiming: "Spain doesn't surrender" hung from a building occupied by the far-right, xenophobic group Hogar Social.
People leant out of windows and cheered as dozens of protesters holding flags of the Spanish Legion, an army unit, and the small, far-right party National Democracy marched up, flanked by police.
Back on the square, Jorge Marin, a 38-year-old engineer, said: "In the end, this is going to come to nothing."
"The Catalans aren't serious, and we're not serious, because they're not really getting independence, and we're not going to put them in prison for what they're doing."