RIA Novosti said the red Communist flag predominated but nationalists and democrats were also in attendance at the Russia Day rally. The March of Millions was approved for 50,000 participants. Crowd estimates ranged from 18,000 to 100,000.
"While we are united, we can never be defeated," RIA Novosti said a crowd chanted.
"They will not scare us!" chanted protesters in reference to a recent increase in fines for protest-related offenses.
This was the first rally since May 6 when a protest in Bolotnaya Square ended in clashes with police and the arrest of some 650 people.
Protest leaders Alexei Navalny, Sergei Udaltsov, Ilya Yashin and Ksenia Sobchak were summoned for questioning Tuesday in the May 6 arrests. Navalny, Yashin and Sobchak obeyed the summons while Udaltsov opted to attend the March of Millions rally instead.