Officers in riot gear had earlier moved into the capital and warned people not to protest. Russian news agency TASS reported that one police officer had been injured while making an arrest.
But protesters also reported mistreatment at the hands of police.
Footage broadcast on Russian television and shared on social media showed police pin people to the ground, kicking or using batons on them. One man told Dozhd TV channel that one such person had been removed from the police van for a beating after asking officers to identify themselves.
Banned from rallying, the organisers designated this a Saturday “stroll” with multiple gathering points along Moscow’s boulevard ring.
So it wasn’t always obvious who was protesting. The old ladies on the benches? The man walking his dog? The food delivery man, right in the middle of it?
To the riot police, out in huge numbers in helmets and body armour, it didn’t seem to matter much. They erected metal barriers and blocked off roads.
Then a woman’s voice came over a loudspeaker, to declare that the security forces included conscripts. “Your sons are among them!”, she said. Then those conscripts – and the professionals – swooped and grabbed people. I saw one man being carried off upside down still strapped to his bicycle.
Once again, hundreds have been detained. This time, though, the police mostly kept their batons buckled to their belts. But the defiance I heard from protesters suggests they’ll be back.
Alexander Svidersky, a member of a district electoral commission, said he was arrested while out with his dog, which he managed to pass off to an acquaintance before being bundled into a police van. OVD-Info reported he said he was later taken out and hit around the kidneys before being dragged to another van.
Detainees at one police station also told OVD-Info they were threatened with having their fingers “cut off” if they did not allow their fingerprints to be taken.
What happened to Lyubov Sobol?
Ms Sobol, a lawyer and video blogger, is one of the candidates excluded from the local elections. She has been on hunger strike for 21 days, and called on others to join the unsanctioned protest on Saturday.
She was in a taxi about to set off for the rally when police officers dragged her into a black van.
Election authorities have barred opposition candidates from taking part in Moscow city authority elections planned for 8 September.
Officials said many of the signatures required for their candidacy applications were invalid. But protesters say they were excluded for political reasons.
Another protest held in solidarity in St Petersburg on Saturday had some 1,000 attendees – but it had not been banned by local officials, and there are no reports of arrests.
What’s been happening in Moscow?
Authorities have launched an investigation into the protests.
On Friday, they detained a number of men – including Alexey Minyaylo, an independent politician and aide to Ms Sobol – in connection with the “mass unrest”, a charge which carries a sentence of up to 15 years in jail.
Opposition politician Konstantin Yankauskas, who is one of the banned election candidates, completed a seven-day jail sentence on Saturday – and was immediately re-arrested as he left the detention facility.
Alexei Navalny has also been arrested in connection with the rallies.
He fell ill in jail with a swollen face and rashes over his body, and was briefly hospitalised.