By John Simpson
BBC World Affairs Editor, Hong Kong
Hong Kong is the only part of China allowed to hold political protests because of its separate legal system
It was the strongest possible answer by the pro-democracy movement in Hong Kong to the Chinese government's efforts to sweep the memory of the Tiananmen massacre under the carpet.
A huge crowd, which the organisers said numbered 150,000, gathered at Victoria Park in Hong Kong to remember the anniversary of the massacre on 4 June 1989. That would make it the biggest anniversary commemoration of all here.
Among the crowds sitting quietly on the ground, with candles in front of them, were some tourists from mainland China. Some who were from Hong Kong had come here every year since the massacre happened. Quite a few were not even born then.
"I am a politics student," one nineteen-year-old said. "I have to know what happened." An older woman said she was always hoping that the Beijing government would apologise for the massacre.
But at present, far from apologising, it does not even admit that a massacre took place - not, at any rate, in the square itself. But those of us who were there saw with our own eyes that dozens of people were shot down in Changan Avenue, which leads to Tiananmen Square.
Altogether, throughout China, the death toll was probably well over 1,000. But no-one knows because the Chinese authorities have never fully admitted to any of it.
They must have hoped that memories of the demonstration and the killings that ended it would have faded long ago. Similar outrages have faded quickly from the world's mind.
But Tiananmen was different. The students captured the sympathy of people around the world, though in China itself many felt that their protest endangered the very definite gains that had already been made. Others saw it as a sign of dangerous chaos.
In China itself, it has not been forgotten, even though it is never referred to in public. The whole episode showed the Communist Party at its weakest.
Things have changed extraordinarily in China over the past 20 years. The economic reforms that have been introduced have gone far beyond anything most of the students hoped for in 1989.
But the Communist Party has never quite dared to make the political changes they wanted. It remains deeply worried about any organised opposition. And it can be brutally heavy-handed when it feels threatened.
By banning any kind of commemoration of the Tiananmen massacre in mainland China, the authorities may have hoped they had dealt with it: not elegantly, perhaps, but effectively. If so, they forgot about Hong Kong.
Here, people have remembered it more intensely than ever. And in Victoria Park they have rekindled the memories of others, all round the world.