The crowds came out in their hundreds of thousands and called for freedom. Truly, this was a defining moment in the history of post-election Iran, writes Robert Fisk

It was Iran's day of destiny and day of courage. A million of its people, marched from Engelob Square to Azadi Square — from the Square of Revolution to the Square of Freedom — beneath the eyes of Tehran's brutal riot police. The crowds were singing and shouting and laughing and abusing their ‘president' as “dust”.

Mir Hossein Mousavi was among them, riding atop a car amid the exhaust smoke and heat, unsmiling, stunned, unaware that so epic a demonstration could blossom amid the hopelessness of Iran's post-election bloodshed.

He may have officially lost last Friday's election, but yesterday was his electoral victory parade through the streets of his capital.

It ended, inevitably, in gunfire and blood.

Not since the 1979 Iranian Revolution have massed protestors gathered in such numbers — or with such overwhelming popularity — through the boulevards of this torrid, despairing city. They jostled and pushed and crowded through narrow laneways to reach the main highway and then found the riot police in steel helmets and batons lined on each side. The people ignored them all. And the cops, horribly outnumbered by these tens of thousands smiled sheepishly — and to our astonishment — and nodded their heads towards the men and women demanding freedom.

Their bravery was all the more staggering as many had already learned of the savage killing of five Iranians on the campus of Tehran University, done to death — according to students — by pistol-firing ‘Basiji' militiamen. When I reached the gates of the college yesterday morning, many of the students were weeping behind the iron fence of the campus, shouting “massacre” and throwing a black cloth across the mesh. That was when the riot police returned and charged into the university grounds once more.

At times, Mousavi's victory march threatened to crush us amid walls of chanting men and women. They fell into the storm drains and stumbled over broken trees and tried to keep pace with his vehicle, vast streamers of green linen strung out in front of their political leader's car. They sang in unison, over and over, the same words: “Tanks, guns, Basiji, you have no effect now.”

As the government's helicopters roared overhead, these thousands looked upwards and bayed above the clatter of rotor-blades: “Where is my vote?”

Cliches come easily during such titanic days but this was truly a historic moment.

Would it change the arrogance of power which Mahmoud Ahmedinejad demonstrated so rashly just a day earlier when he loftily invited the opposition — there were reported to be huge crowds protesting on the streets of other Iranian cities yesterday — to be his “friends”, while talking ominously of the “red light” through which Moussavi had driven.

Ahmedinejad claimed a 66% victory at the polls, giving Mousavi scarcely 33%. No wonder the crowds yesterday were also singing — and I mean actually singing in chorus — “They have stolen our vote and now they are using it against us.”