Read more of Slate's coverage of the Egyptian protests.
The last line of defense is human. Men link arms to form a human wall across the broad boulevard. People passing into the square are asked for ID and patted down. "We found weapons inside the square," the young woman who frisked me said. "We don't know where they are coming from."
Behind the line of men is a makeshift clinic. As I walk by, a man who was a Muslim Brotherhood candidate in Egypt's parliamentary elections walks by with his followers. After him, a line of professors from Al Azhar University, the Islamic world's most prominent institution of learning, walk forward, linking arms.
Back inside the square, all is calm as protesters continue to flock to the square. The loudspeaker that is used to keep up morale also announces the names of the missing. Volunteers continue to bring in water, juice, and food, but there seems to be less available today, and it's hot, so people are thirsty. Later I hear that plainclothes police prevented many from bringing in supplies.
"It's like a utopia here. We're really organized. We have a self-sustaining city. At 6 a.m. there is a fuul cart, [fuul is a popular Egyptian dish], a kiosk selling cigarettes, people are passing out food and water, [there's] a night watch," Nazly tells me.
As we sit on the ground, a man walks by holding a trash bag. He yells the name of Mubarak's ruling party as he calls for rubbish: "National Democratic Party! National Democratic Party!"
As the day drags on, and Mubarak clings to power, the atmosphere is buoyant. But whether the besieged protesters can maintain their city within a city is another story. Once again today, everyone repeats that they'll stay until the bitter end.
As I exit the square, I step over neatly arranged rows of rocks. Men sit on the sidewalk perusing newspapers. It's all calm until the battle cry sounds.