Gunfire erupted when the protesters reached the square; it was sporadic at first, then more sustained. Security forces fired into the surrounding streets leading into the traffic roundabout.
Ambulances raced to the scene but had difficulty reaching those who had fallen in the barrage of bullets and tear gas, said marchers who made their way to the hospital with the injured.
"Everybody was on the ground. They were shooting at the heads and chest," said Mohamed Nabi, 27, who was with two friends in the emergency room. "We were chanting, 'Peaceful, peaceful!' but the government was willing to have a massacre. We weren't afraid. We were willing to die in this way."
Ali Hasan Arafat lay bare-chested on a stretcher, breathing heavily from the effects of tear gas. The gas was so caustic, he said, that he was blinded and ran into a signpost, injuring his head.