By John Simpson
BBC World Affairs Editor, Tehran
Iranian schoolgirls celebrating the 30th anniversary of the 1979 revolution
Since the cold day in February 1979 when the crowds stormed the police and army buildings and the Shah's last forces surrendered, Iran has been through a torrid time: war, terrorism, isolation, confrontation, sanctions.
Most people in the West assumed that the Islamic revolution would collapse fast.
Even a few months ago, the possibility existed that either Israel or America would soon bomb Iran. There was fresh talk of "regime change".
Yet the revolution which has survived for three long decades shows no sign of going away. The vast crowds which gathered in Freedom Square to celebrate were good-humoured and reasonably enthusiastic.
And there was relief and pleasure when President Mahmoud Ahmadinejad was much more positive about President Barack Obama's olive-branch.
In spite of the regular chants of "Death to America", most people here would probably prefer it if Iran's relations with the US were a lot warmer.
Thirty years ago, when I was in Freedom Square covering the revolution, the crowds were wild with expectation; they felt that the political and religious millennium was just around the corner.
They know better now. Yet most of the people I spoke to as they swarmed around the same monument were still reasonably enthusiastic.
(For the record, people here worry less than they used to about speaking in public to foreigners. There is a little less snooping now than there used to be - though not for bloggers, who can have a very unpleasant time here.)
Iranians hold up photos of Iran's late leader Ayatollah Khomeini
There was plenty of official encouragement to come to the demonstration, certainly.
But it was nothing like the old Soviet system, or Saddam's Iraq, where you would be punished for refusing to turn out. These people were the bed-rock of President Ahmadinejad's support.
The vast majority came from the working-class areas of Tehran, areas which will vote loyally for him at the next presidential election in June. That is despite the very real danger of an economic collapse here, with the sudden fall in the oil price.
There were only a few middle-class people at the rally. A sizeable proportion of them would probably feel there was nothing very much to celebrate in 30 years of Islamic rule. The constant niggling intrusions into people's private life are less now than there were a year ago, but they still exist.
As the election comes closer, you see more women wearing make-up in the streets, more couples holding hands. President Ahmadinejad is unwilling to alienate people unnecessarily.
On the one hand, a better relationship with the Obama administration would make Iranians feel more relaxed, and easier with their own government. On the other, it could lead to greater American influence in everyday life; and that would be a problem for the government.
Dolce and Gabbana
Yet that problem exists already. At the big rally in Freedom Square, I spent a lot of time talking to young people.
Two-thirds of Iran's population of 70 million are under the age of 25, and it was a shock to me to see how few of the people who had turned out to celebrate the 30th anniversary of the revolution were actually alive when it happened.
The teenagers and twenty-somethings I spoke to were proud of their country and its achievements, but they scarcely cared about politics at all; especially the elderly clerics who still have a major say in the government.
What does the Islamic Revolution have to offer on its 30th anniversary to a young man of the kind I came across in Freedom Square, with a gallant attempt at a punk haircut, and a Dolce and Gabbana badge on his stylish coat?
After 30 years, probably not an awful lot. He is looking for a rather different kind of freedom. And there are plenty of people like him.