It was hard to spot the protesters at first on Moscow's main street. The vast majority were not carrying placards.
In fact, many were waving or even wearing the Russian flag. Their idea was to walk down Tverskaya Street and protest simply by their presence.
But the demonstration against corruption ended in mass detentions.
We watched as riot police in body armour and helmets formed snatch squads six-men strong, shoved their way into the crowd and grabbed hundreds of protesters at random, sometimes brutally.
The scenario was predictable.
As soon as opposition leader Alexei Navalny called people into the city centre to protest, rejecting the site allocated by the authorities, he was setting the stage for confrontation.
Thousands of people of all ages heeded his call in any case, but many were in their late teens and early twenties. This is a generation that has only ever known one leader - President Vladimir Putin - and some clearly are unhappy with that.
'Not afraid of Putin'
"I came because I don't like Putin and what we see on our TV is completely false. I want to change something," a protester called Kirill told the BBC. He described the event as "successful" despite the detentions.
"A lot of people came. They are not afraid of our police and Putin," he argued.
"The same people have been in power for 17 years. They steal, but nothing works here," a 16-year-old boy told a video team from Vedomosti newspaper. "We young people don't see a decent future."
The Kremlin spokesman shrugged off the protest as a "provocation" and argued that the police had simply restored order.
But the scenes in Moscow led one commentator to warn that Russia's political "temperature" was rising.
"The situation becomes more serious each time," Valery Solovei wrote on Facebook, suggesting more protests and more trouble to come.
Others are talking of a "radicalisation" of society, though those we saw demonstrating on Monday were peaceful.
Navalny team hails protest
The key driver of the protests is Alexei Navalny, the charismatic anti-corruption activist who has declared he will challenge Vladimir Putin for president in next year's election.
The rallies are partly about forcing the Kremlin to let him run, despite a suspended prison sentence for embezzlement, which he insists was politically motivated.
Now, sentenced to 30 days in police custody, he will not get to campaign for a while. But he recorded a typically defiant video statement before he was led out of court.
"I saw the pictures. You were great," Alexei Navalny told protesters. "Carry on working and fighting corruption."
Monday's protest was the second the activist had called in just over two months. The attendance in Moscow this time was lower, but there were rallies right across the country.
Organisers say crowds came out in more than 160 towns, double the number in March.
"That showed the strength of our campaign," Mr Navalny's campaign manager told the team's YouTube channel, calling it the biggest "synchronised protest" since the 1990s.
"The whole country rose up... against corruption and injustice," Leonid Volkov claimed.
Critics scoffed at such talk.
The Moscow city government official responsible for security said no more than 5,000 people had protested in the capital. Compared with some 2.5 million people who had joined Russia Day celebrations, he called that a "paltry percentage".
Some here accuse Alexei Navalny of "sacrificing" young protesters in his own drive for power. Plenty, even in the opposition, disagree with his confrontational style and methods.
But the activist's campaign to expose and fight corruption at the highest level is proving a powerful rallying call.
"I want to live in better conditions," another young man told the BBC, amid the crowd shouting "Russia will be free!" on the road that leads down to the Kremlin.
"I think our government can react," he said. "They must give us answers for their corruption; for their actions."