The Kremlin-friendly novelist Sergei Minaev warned protesters that if they died there, even their close friends would forget the cause for which they had laid down their lives. “If I believed in God,” wrote the liberal politician Leonid Gozman on the eve of the gathering, “I would pray to him to bring reason to the generals, and, more importantly, to those who give them orders.”

What occurred, of course, was something fundamentally, jarringly different.

To anyone who has spent time in Mr. Putin’s Russia, the sight that unfolded on Bolotnaya Square on Dec. 10 came as an almost physical shock. It has been so long since Russians went out in the streets in large numbers demanding political change that the crowd — an estimated 50,000 people, calmly watched over by the police — resembled a natural wonder, like the aurora borealis.

People in the crowd, instead of listening to the speakers, most of whom had the tinny vehemence of party agitators, were peering around at each other. They were neither wild-eyed nor downtrodden. They did not smell of fear or aggression. The critical mass of middle-class professionals that has existed on the Internet for years was suddenly a physical fact, close enough to feel the body heat. It seemed like the birth of a new organism.

Nothing scary happened that day, or at a repeat demonstration on Dec. 24, when the crowd was significantly larger. Yevgeny S. Gontmakher, an economist who has advised the government on social unrest, said that Russian leaders had no formula for dealing with protesters whose demands cannot be addressed with money, because that kind of crowd has not existed here, as a rule. That it has appeared now “is a sign that Russia is becoming a Western country, in its own way.”

“It’s public politics,” Mr. Gontmakher said. “It is no longer marginal to be involved in public politics. I think this is happening for the first time in Russia. It suggests that Russia has to choose a European path. People say Russia is not Europe. No — Russia is Europe.”

It may be that these latest protests have marked a change in the relationship between the Kremlin and crowds.

After an initial burst of acid hostility, Mr. Putin and his officials began to speak of the protesters with a modicum of respect, perhaps because it became clear that they represent a wide swath of the capital’s media and business elite. Last week, Vladislav Y. Surkov — the Kremlin official who for 10 years made it his business to stifle any street politics that might grow into a threat to Mr. Putin — said the protesters at Bolotnaya represented “the best part of our society, or, more accurately, the most productive part.” (Mr. Surkov was reassigned to a nonpolitical position a few days after his remarks were published.)