Violence flared as tens of thousands descended on Madrid, some having trekked from the furthest corners of Spain, at the end of a month-long "march for dignity" against the dire state of the economy.
What had been a day of largely peaceful demonstration took a violent turn late on Saturday, as dozens of youths smashed the windows of a bank, set garbage bins on fire and threw projectiles at police, who responded by firing rubber bullets and charging.
Earlier in the day, eight columns had converged on the capital at the culmination of nearly a month of walking for some of the protesters.
They were carrying flags from Andalucia in the south, Catalonia in the east, or the Asturias in the northwest.
"Rise! Rise! We will fight!" chanted one group gathered at Atocha station before heading down the broad avenues of Madrid's city centre.
The "march for dignity" comes after two years of bruising austerity measures, forced on Spain as part of a €40 billion (HK$428 billion) international bailout after a huge housing bubble almost destroyed its banking system.
Austerity has left Spain in a prolonged economic funk, with more than 26 per cent of the population - and half of under-25s - out of work.
Meanwhile, say many of the protesters, the corrupt collusion between officials and bankers that caused the crisis has gone largely unpunished.
They were joined by many civic groups that emerged out of the mass Indignados protests of 2011 and 2012 when the crisis first hit Spain.
The Indignados were seen as forerunners of the Occupy movement that spread around the world.
On Saturday, the organisers hired hundreds of buses and at least four trains to transport protesters, while the government deployed about 1,700 police.
The unprecedented austerity package imposed by the right-wing government of Prime Minister Mariano Rajoy after its election in late 2011 was considered vital to bringing Spain's huge debts under control and restoring confidence in its shattered banking system.
But spending cuts of €150 billion have done nothing to dent Spain's record levels of unemployment and prolonged recession,
They also triggered two general strikes in 2012 that brought millions to the streets.
"Let them give us the money stolen by politicians and bankers," said protester Trini Reina, 48, from Seville.
"I haven't paid my mortgage for seven months. The system is bankrupt and we are paying dearly for it."