In global terms it was not the biggest demonstration. The police put it at 25,000, though it may have been double that.
But for Russia in the apathetic 21st Century this was a huge protest, and it will have shaken the political establishment.
For 12 years many people here have stayed indoors when demonstrations were organised.
They put politics on the back burner. They concentrated on stabilising their lives after the control-freakery of the Soviet Union and the chaotic 1990s. They were happy to buy a new car, and get a new job.
But when these elections came round people decided to get back some control over their country. They felt the political elite had been taking advantage of their apathy. So, in large numbers - and particularly in Moscow - they voted against the ruling party, United Russia.
Then came the results, and they believed they had been cheated. Today at the Moscow demonstration they told us that was why they took to the streets. They said it was the internet videos of ballot-stuffing, vote-stealing, and blatant forgery of official results that drove them mad.
As the light early-winter snow swirled around her black fur hood, Yelena Konchalovskaya, an 18-year old theatre student said, "I was just really shocked about - like - how big the falsification was, and I'm not OK with that."
Gera Pavelov, 21, is studying architecture. "I want to have fair elections in my country," he explained. "I don't know any single person who voted for United Russia, so I doubt that they got 45% in Moscow."
New problem generation
They were typical of a good proportion of the crowd. Young, well-educated, and well-connected to the world through the internet.
This was Russia's social network moment. The country's unloved opposition parties suddenly found themselves talking to tens of thousands of new faces at a rally, people that had been inspired by Twitter, Facebook, Vkontakte and Livejournal.
This was also, possibly, the moment that some in one of the "official" opposition parties woke up.
The Just Russia party was invented by Vladimir Putin's Machiavellian advisers to take votes from the Communists. But today Gennady Gudkov, a Just Russia deputy who has become furious at the rampant corruption, was prominent at the demonstration.
He too was complaining about the election result. "It doesn't respect the results of real people power," he said "That's why we are here. Not only we. Tens of thousands of people."
Some of the crowd were a mix of old-time radicals, and the revolutionaries of 1991 who overthrew Communist Party rule.
But they are not the people Mr Putin needs to fear. His new problem is the ipad generation, who have listened to their parents complaining for the last 12 years about the loss of freedoms, the rigged elections, the corruption, and the state-controlled television.
It may be that they will now decide to do something about it.
It may not be immediately. It may not even be next year. But if they get the taste for protest, and get a feeling for their power when they act together in large numbers, Mr Putin could suddenly find he has a rebellious electorate on his hands.
That is something he has never experienced before. We have not got there yet however.
Today the crowd had one simple demand: "New elections!". But even meeting that demand - with the current mood in the capital - could itself be a very risky strategy.