Anti-Putin protesters show their strength in Russia
"We will come here as if to work. It must be part of our everyday life," said Alexei Navalny, an opposition blogger and protest organizer. "I want each of us to ask ourselves when we look in the mirror in the morning what we can do for freedom."
Riot police were out in force but stood by watching for most of the day, until witnesses said they detained Udaltsov and several others around 10 p.m. (1800 GMT), the time by which city authorities had said the eight-hour protest must end.
The protesters say Putin's return to the Kremlin after four years as premier is a setback for democracy. He could now extend his rule of Russia to 24 years if he wins another term when his mandate expires in 2018.
This would mean ruling longer than Soviet leader Leonid Brezhnev, and opponents fear political and economic stagnation.
"People who lived in the Soviet Union are tired of absolute rulers. We're tired of a police state," said Alexander Kokhmansky, 79, as he marched.
Sergei Yevseyev, 35, said he was protesting against "the total lawlessness, total corruption, the lack of civil freedoms, the absence of independent courts and social injustice."
There was also more focus on social problems than at previous protests, and more communists marched this time with nationalists, liberals, gay rights campaigners and leftists.
Other marchers wanted to show solidarity, without being confident the opposition can achieve much after failing to select a leader or touch off protests outside the big cities. Continued...