Her screams were not drowned out by the clamor of the crazed mob of nearly 200 men around her.
An endless number of hands reached toward the woman in the red shirt in an assault scene that lasted less than 15 minutes but felt more like an hour.
She was pushed by the sea of men for about a block into a side street from Tahrir Square. Many of the men were trying to break up the frenzy, but it was impossible to tell who was helping and who was assaulting.
Pushed against the wall, the unknown woman's head finally disappeared. Her screams grew fainter, then stopped. Her slender tall frame had clearly given way. She apparently had passed out. The helping hands finally splashed the attackers with bottles of water to chase them away.
The assault late Tuesday was witnessed by an Associated Press reporter who was almost overwhelmed by the crowd herself and had to be pulled to safety by men who ferried her out of the melee in an open Jeep.
Reports of assaults on women in Tahrir, the epicentre of the uprising that forced Hosni Mubarak to step down last year, have been on the rise with a new round of mass protests to denounce a mixed verdict against the ousted leader and his sons in a trial last week.
The late Tuesday assault was the last straw for many. Protesters and activists met Wednesday to organize a campaign to prevent sexual harassment in the square. They recognize it is part of a bigger social problem that has largely gone unpunished in Egypt.
But the phenomenon is trampling on their dream of creating in Tahrir a micro-model of a state that respects civil liberties and civic responsibility, which they had hoped would emerge after Mubarak's ouster.
"Enough is enough," said Abdel-Fatah Mahmoud, a 22-year-old engineering student, who met Wednesday with friends to organise patrols of the square in an effort to deter attacks against women.
"It has gone overboard. No matter what is behind this, it is unacceptable. It shouldn't be happening on our streets let alone Tahrir."
No official numbers exist for attacks on women in the square because police do not go near the area, and women rarely report such incidents.
But activists and protesters have reported a number of particularly violent assaults on women in the past week. Many suspect such assaults are organised by opponents of the protests to weaken the spirit of the protesters and drive people away.
Mahmoud said two of his female friends were cornered Monday and pushed into a small passageway by a group of men in the same area where the woman in the red shirt was assaulted.
One was groped while the other was seriously assaulted, Mahmoud said, refusing to divulge specifics other than to insist she wasn't raped.
Mona Seif, a well-known activist who has been trying to promote awareness about the problem, said Wednesday she was told about three different incidents in the past five days, including two that were violent.
In one incident, the attackers ripped the woman's clothes off and trampled on her companions, she said.
Women, who participated in the 18-day uprising that ended with Mubarak's 11 February 2011 ouster as leading activists, protesters, medics and even fighters to ward off attacks by security agents or affiliated thugs on Tahrir, have found themselves facing the same groping and assaults that have long plagued Egypt's streets during subsequent protests in the square.
Women also have been targeted in recent crackdowns on protesters by military and security troops, a practice commonly used by Mubarak security that grew even more aggressive in the days following his ouster.
In a defining image of the post-Mubarak state violence against women, troops were captured on video stomping with their boots on the bare chest of a woman, with only her blue bra showing, as other troops pulled her by the arms across the ground.
A 2008 report by the Egyptian Center for Women's Rights says two-thirds of women in Egypt experienced sexual harassment on a daily basis.
A string of mass assaults on women in 2006 during the Muslim feast following the holy month of Ramadan prompted police to increase the number of patrols to combat it but legislation providing punishment was never passed.
"If you know you can get away with sexual harassment and assault, then there is an overall impunity," Human Rights Watch researcher Heba Morayef said.
The case is more paradoxical in Tahrir, which has come to symbolise the revolution, but has lost its original lustre among Egyptians weary of more than a year of turmoil.
Women say they briefly experienced a "new Egypt," with strict social customs casually cast aside during the initial 18-day uprising — at least among the protesters who turned the square into a protected zone.
But that image was marred when Lara Logan, a U.S. correspondent for CBS television, was sexually assaulted by a frenzied mob in Tahrir on the day Mubarak stepped down, when hundreds of thousands of Egyptians came to the square to celebrate.
The post-Mubarak political reality for women also has deteriorated.
They have lost political ground in the 16 months since Mubarak's ouster — even winning fewer seats in parliament in the first free and fair elections in decades.
The 508-member parliament has only eight female legislators, a sharp drop from the more than 60 in the 2010 parliament thanks to a Mubarak-era quota. Women's rights groups also fear the growing power of Islamist groups will lead to new restrictions.
Activists have no idea what finally happened to the woman in the red shirt. But they have been alarmed by the rise in violent attacks on women, which has chipped away at efforts to project the square as a utopia free of discrimination and violence.
Seif said there is a responsibility inside the square.
"I think it is getting worse because people don't want to acknowledge it is happening or do something to reduce it," said Seif. "It is our job to put an end to it, at least in Tahrir."