Tens of thousands of Russians have flooded Moscow's tree-lined boulevards in the first massive protest against president Vladimir Putin's rule since his inauguration in May - a rally that came even as police interrogated key opposition leaders.
Since embarking on his third presidential term, Mr Putin has taken a stern stance towards the opposition, including signing a repressive new bill last week introducing heavy penalties for taking part in unauthorised rallies.
Police on Monday searched opposition leaders' apartments, carting away computers, mobile phones and other personal items. They also demanded that opposition leaders attend for questioning on Tuesday, just an hour before the rally began - widely seen as a crude attempt by the government to scare the protesters.
The march was being held on Russia Day, a national holiday that honours June 12, 1990, when Russian members of parliament decided that Russian laws should take priority over Soviet Union laws. The Soviet Union collapsed in 1991.
Left-wing politician Sergei Udaltsov snubbed the summons, saying he considered it his duty to lead the protest as one of its organisers. Russia's Investigative Committee said it would not immediately seek his arrest but would interrogate him later.
Anti-corruption blogger Alexei Navaly, liberal activist Ilya Yashin and TV host Ksenia Sobchak showed up for the interrogations, preventing them from attending the demonstration.
Investigative Committee spokesman Vladimir Markin said authorities had found a large amount of cash at Ms Sobchak's apartment and would initiate a check to see whether she had paid her taxes.
Ms Sobchak, the only daughter of St Petersburg's late mayor, a man who was Mr Putin's mentor, had been spared reprisals until Monday's raid. "I never thought that we would slide back to such repressions," she tweeted on Monday.
Braving a brief thunderstorm, protesters showed up on the landmark Pushkin Square ahead of the planned march and their numbers grew as they began marching down boulevards to a broad central avenue where a rally was being held. Despite fears following a violent police crackdown on a previous protest last month, the demonstration went on peacefully.
Speaking at the rally, Mr Udaltsov reaffirmed a call for early presidential and parliamentary elections. He put the number of protesters at 100,000, while police estimated that about 20,000 showed up.