They were all armed with grievances, though some conceded that they had fewer complaints than others. “I don’t have economic problems,” Tarek Tohamy, an engineer, said as he walked toward checkpoints that led to the square. “I have a nice car. I have a villa.”

But Mr. Tohamy was alarmed by Egypt’s dismal condition, and concerned about the country he was leaving to his daughter.

At one point during last week’s protests, he said, he started to feel sorry for Mr. Mubarak, saying he was a war hero. “He’s part of our history,” Mr. Tohamy said.

That feeling did not last long, and before Tuesday night’s announcement, Mr. Tohamy found himself needing a clear signal of Mr. Mubarak’s intentions.

“We can go into history, or we can go in the garbage of history,” Mr. Tohamy said.

The gathering was a carnival with an edge. A teenage girl led her friends in a chant: “Egypt’s free, and Mubarak’s out.” A crowd gathered around a man who said he was a former political prisoner, leaning in to listen as he talked about the insects in the prison food. There were several good-natured arguments, and at least one scuffle, after a crowd confronted a man they said belonged to the secret police.

A group of men said they had been sleeping in the square for days.

“In liberation, until liberation,” one of them said. His friend, playing on a familiar theme, begged Mr. Mubarak to leave so he could go home.

The gathering spilled its banks, as small demonstrations moved to nearby Talaat Harb Square. There, Ahmed Zidan held a sign that said “This is Egypt, not Iran.” He said he meant that Egyptians had no interest in an Islamic state, an assertion repeated by a number of protesters, many of whom also said any government should include members of the Muslim Brotherhood.