In other cities, protesters clashed with the president's supporters, and broke into or set fire to the local headquarters of the Muslim Brotherhood or its political party, the Freedom and Justice Party, in at least three cities.
The Tahrir demonstrations, the biggest since President Morsi took office, were a powerful rejection of the president's decision to sideline the judiciary, which had remained nearly the only check on his power. He already holds both executive and legislative authority.
"This decision is unjust. It makes Morsi into another dictator," says Rabab el Khatib, a doctoral student in economics, in Tahrir. She said the large turnout would force Morsi to retract the decision. "The Muslim Brotherhood must know that they are not the only ones in Egypt," she says, referring to the Islamist movement Morsi hails from. "The Egyptian people are much more than the Brotherhood. We are here, and we are strong, and we will not accept this decision."
Morsi has signaled that he won't back down, with a presidential spokesman insisting to reporters that the president's new powers are temporary and necessary to allow a constitution to be written and a parliament election.
Demonstrators reveled in the fact that they had achieved such high turnout without Islamist participation. Since Mubarak's fall, protests that do not include the Muslim Brotherhood have struggled to match the turnout of those promoted by the highly organized group. Tonight, vendors sold roasted sweet potatoes and koshari, an Egyptian pasta dish, to the crowds that included men, women, and children from across the spectrum of Egyptian society. Some said the protest reminded them of the days of the uprising that ousted former President Hosni Mubarak in February 2011.
Protesters repeated the same chant that became famous during those protests: "The people want the fall of the regime." Some demonstrators said they had one main demand: that the president revoke the constitutional declaration that expands his power. But others called for his ouster, changing the chant to "The people want the end of Morsi's rule."
Morsi issued a constitutional declaration last week that shields his decisions from judicial review until a new constitution is in place. He also declared that the committee drafting a new constitution is immune from court rulings that might dissolve it. The president says his decision was the only way to keep Egypt on the path toward stability, and emphasized that his powers are only temporary.
Protester Ahmed Salah, a lawyer, said the decree is an assault on judicial independence. He says it concentrates too much power in Morsi's hands.
"He will be worse than Mubarak, because he wants to use his power to benefit the Muslim Brotherhood and make sure they stay in power for 50 years," he says.
Some of those in the square voted for Morsi when he ran for president against Ahmed Shafiq, the last prime minister under Mubarak. Hisham Ali said he did so because he thought it was the only way to keep the revolution alive. Now, he says, Morsi has turned against the very essence of that uprising.
"He has turned into a dictator, like the one we came here to get rid of," he says.
Rumors spread in the crowded square that the minister of justice or the minister of interior had resigned, and protesters called friends to check the news, shouting into their phones to be heard above the din.
Wary of being cast as as supporters of the old regime, others chanted slogans against the "feloul," a word that literally means "remnants" and has come to represent those who were a part of or supporters of Mubarak's regime.