The street protests broke out after a December parliamentary election won by Putin's party through what observers said was widespread fraud, and they grew in strength ahead of Putin's effectively unopposed election in March to a third presidential term.
Huge rallies of more than 100,000 people even in bitter winter cold gave many protesters hope for democratic change. These hopes have waned, but opposition supporters appear ready to dig in for a long fight.
"We have to defend the rights that we were deprived of, the right to have elections. We were deprived of honest elections and an honest government," opposition activist Alexander Shcherbakov said. "I've come to show that and to demonstrate that the people are opposed. I'm opposed to the illegitimate government and illegitimate elections."
Leftists, liberals and nationalists mixed with students, teachers, gay activists and others as they marched down Moscow's tree-lined boulevards chanting "Russia without Putin!" and "We are the power here!" Many wore the white ribbons that have become the symbol of the protest movement.
About 7,000 police officers stood guard along the route of the march, and a police helicopter hovered overhead. A protest rally, held on a wide street named for the late Soviet dissident Andrei Sakharov, remained peaceful as it stretched into the evening. As the 10 p.m. deadline neared, a couple of hundred people were still on the street and police herded them toward a subway station. One of the opposition leaders, Sergei Udaltsov, was detained along with a handful of his supporters when he tried to lead a group of about 50 on a new protest march.
Putin has shown less tolerance for the opposition since his inauguration in May. New repressive laws have been passed to deter people from joining protests, and opposition leaders have been subject to searches and interrogations. In August, a court handed down two-year prison sentences to three members of the punk band Pussy Riot for performing an anti-Putin song inside Moscow's main cathedral.
Big balloons painted with the band's trademark balaclava masks floated over the crowd on Saturday, while some rally participants wore T-shirts in support of Pussy Riot.
Many demonstrators targeted Putin with creative placards and outfits. Some mocked Putin's recent publicity stunt in which he flew in a motorized hang glider to lead a flock of young Siberian white cranes in flight.
One protester donned a white outfit similar to the one worn by Putin on the flight with a sign reading: "Give up hope, each of you who follow me." Another person held a placard that said: "We are not your cranes."
Alexei Navalny, a charismatic anti-corruption crusader and a popular blogger, remains the rock star among the protest leaders. When he took the stage, young people in the crowd held up their phones to record the moment.
Navalny urged the demonstrators to show resolve and keep up the pressure on the Kremlin with more street protests.
"We must come to rallies to win freedom for ourselves and our children, to defend our human dignity," he said to cheers of support. "We will come here as to our workplace. No one else will free us but ourselves."
The rally appeared as big as the last major protest in June, which also attracted tens of thousands. More of the demonstrators, however, came not as members of the varied political organizations that make up the protest movement, but with groups of friends and co-workers, some of them organizing on social networks.
As part of a new initiative, activists collected contact information and addresses from demonstrators to make it easier to organize civic actions on a neighborhood level.
Gleb Pavlovsky, a former Kremlin political consultant, who attended Saturday's rally, estimated that up to 500,000 people have taken part in the protests in Moscow, a city of 11.5 million.
He said the Kremlin has not figured out how to deal with the protest movement.
"Therefore, they alternate between taking tough action and stepping back from confrontation," Pavlovsky said. "For the Kremlin, it is very worrying that Moscow no longer supports Putin, but it is very important that this is purely a Moscow phenomenon."
Although opposition protests also were held Saturday in several other Russian cities, the largest, in St. Petersburg, drew only a few thousand people. Protests elsewhere attracted only hundreds or even dozens. About 100 attended an unsanctioned rally in Nizhny Novgorod and about 20 of them were detained.
The Moscow organizers had spent days in tense talks with the city government over the protest route for Saturday, typical of the bargaining that has preceded each of the opposition marches.
A protest on the eve of Putin's inauguration ended in clashes with police, and the Kremlin responded by arresting some of the participants and approving a new draconian law that raised fines 150-fold for taking part in unsanctioned protests. The city, however, granted permission for the subsequent opposition rally in June, which was peaceful.
A day before the weekend rally, parliament expelled an opposition lawmaker who had turned against the Kremlin and joined the protest movement. Anger over the ouster of Gennady Gudkov may have helped to swell the ranks of the protesters.
"Russia no longer has a constitution," Gudkov told the rally. "Russia no longer has rights, and Russia no longer has a parliament worthy of respect. Shame on this parliament, and shame on this government!"
Gudkov's expulsion also means he loses his immunity from prosecution, and his supporters fear he could face arrest.
His son, Dmitry Gudkov, also a lawmaker, said he hopes the Kremlin will think twice about arresting his father after seeing the size of the protest. "They will either have to think about serious reforms and end their repressions, or they will come to a very bad end," he said as marched with a column of protesters.
"It's necessary right now for all Russians to come out into the streets to show the regime that changes are needed in our country, and that without them our country can't develop," said teacher Valentina Merkulova, who participated in Saturday's protest. "The most important thing is that, the more Russians come out, the less bloody the change of regime, the change of power. A change of power is necessary."