A female protestor chimed in, saying, "We're here for our revolution." Like many here, she expressed the hope that the demos can bring about a change in the government.
In the midst of these demos, there are some signs of the government ceding ground. In a completely unexpected development, Iran's Guardian Council announced a recount of the presidential vote, raising the possibility that the outcome may be overturned.
But state television quoted a council spokesman saying the recount would be limited to polling stations where candidates claim irregularities took place.
Iran's ruling Guardian Council calls the results provisional.
Protesters sent out another round of Twitter messages Tuesday, announcing plans to hold another rally. "Alert: Mousavi march still on 5PM," one message read, Reuters reported.
Mousavi and two other moderate candidates contesting the election results are scheduled to meet members of the Guardian Council today. They have been calling for the election results to be voided and a new election held.
Monday, Mousavi supporters flooded through downtown Tehran - numbering hundreds of thousands - making this possibly the largest demonstration here since the 1979 Islamic revolution.
The demonstration was officially illegal. The government denied protestors permission but many defied that decision to show support for Mousavi and anger at an election they see as stolen.
Mousavi, making his first public appearance since election day, told the crowd to "stand up to this charade."
All was peaceful until early in the evening pro-government paramilitary fired into the crowd.
The shots came from the roof, an eyewitness told ABC News over the phone, hitting a car with protestors riding on top. One man was hit and flung from the car.
The government blames the violence on the protestors, calling them vandals. But many Iranians don't accept that explanation, and the government now faces an enormous popular wave of dissent.
Violence is now spreading around the country. Mousavi's Web site reports that a protestor has been killed in Shiraz, while the BBC is reporting instances of live fire being used by police in provincial cities.
Protestors are fighting bullets with technology. Wherever we go, we're surrounded by people, like us, filming on their cell-phones, and spreading the word on websites like Facebook and Twitter, which has led government censors to block them.
A Mousavi supporter scoffed at the government, saying "the government thinks that blocking websites can prevent the protests [...] but if people want, they can reach their goals anyway."
And the word still gets out, with amateur videos being posted on YouTube and shown to the world.
And there is another large opposition demonstration planned for today, with supporters of President Ahmadinejad planning their own demo at the same square, setting up the possibility of more clashes.
As unrest grows at home, Ahmadinejad is making his first overseas trip since the hotly contested election, visiting the Russian city of Yekaterinburg. He is attending the Shanghai Cooperation Organization (SCO) summit as an observer. The president told the summit that "the age of empires" had ended, but he made no mention of the protests, even as the international community raises questions about the validity of the election.