The demonstration marked the first anniversary of large opposition protests, RIA Novosti reported. Many of those who came to the square, site of the headquarters of the Federal Security Bureau, left flowers at a memorial to victims of the KGB and the Stalinist gulags.
Police cordoned off the square but did not make any arrests until most of the crowd had departed. The press service of the Moscow Police said they included a number of prominent bloggers and reporters who were charged with incitement, ITAR-Tass reported.
Sergei Udaltsov of the Left Front, who was among those detained, disputed the police estimates of the crowd. He said at least 5,000 people were in the square.