The joy of freedom: 20 years on

It was the same sort of miserable November weather, grey and drizzling; the mass of humanity was large, chaotic and giddy as then; and there in the midst of it, three figures as solidly "eastern" as any of those who teemed across the Berlin Wall 20 years ago.

Lech Walesa, still every inch the Polish shop steward in his unionist's cap, Mikhail Gorbachev, still recognisably the Russian Communist he was then, and Angela Merkel, who when the Wall fell was a humble scientist in East Berlin.

Together they linked arms and walked over the grey steel Bornholmer bridge across which tens of thousands of East Germans, Ms Merkel among them, first flooded into West Berlin on the night of 9 November 1989. Carrying a small white rose and a large umbrella, the German Chancellor – whose life was changed beyond recognition by the Wall's collapse – paid tribute to her companions. "What happened in Poland was incredibly important for us all," she said. And, turning to the former Soviet leader, she said: "We always knew that something had to happen there so that more could change here. You courageously let this happen, and that was much more than we could expect."

The return to the Wall yesterday was low key, but nonetheless emotional. Ms Merkel told the crowd: "This is not just a day of celebration for Germany but for the whole of Europe."

Earlier, during a service at Berlin's Gethsemane church, she acknowledged that, despite the 20 years that have elapsed since the fall of the Wall, Germany still bears the scars of division, with the rate of unemployment in the East double that of the West. "German unity is still incomplete – we must tackle this problem if we want to achieve quality of life on an equal basis," she said.

What happened on the night of 9 November at the Bornholmer bridge crossing point was arguably the single most critical moment in the events of 1989. East German border guards faced a 20,000-strong crowd of East Berliners chanting "Open the gate!" After trying to contact his superior and getting no response, the officer in charge of the crossing point ordered the barriers to be opened. A human tide of East Berliners flooded into West Berlin, and within the hour all of Berlin's seven crossing points were thrown open, heralding the collapse of Communism.

Katrin Hattenhauer, who is now in her early 40s, joined the throng of East Germans who headed for West Berlin across the Bornholmer that night. A dissident who had been jailed in Leipzig, she had only just been released from prison and was officially banned from travelling to Berlin. "I decided to go all the same. It is my birthday on 9 November and I met up with some friends in East Berlin. Suddenly we heard the borders were open," she recalled. "The feeling was overwhelming. I went to the Bornholmer bridge and then on into West Berlin. They were dancing on the Wall. It was the best birthday present I could have had," she recalled.

Ms Hattenhauer was one of hundreds of thousands of Berliners and visitors from across Germany and overseas who joined celebrations in the capital last night. Ms Merkel described the events as "a celebration of the happiest day in post-war German history".

Last night it was still raining as all 27 EU leaders plus Hillary Clinton and President Dmitry Medvedev of Russia gathered under the Brandenburg Gate. Also attending was the former Hungarian prime minister Miklos Nemeth, whose decision to open his country's borders with the West in the summer of 1989 was a key step towards Communism's collapse.

In a special address broadcast to the crowds on video, US President Barack Obama said of the fall of the Wall: "There could be no clearer rebuke of tyranny. There could be no stronger affirmation of freedom."

Ms Merkel led a procession of leaders through the Brandenburg Gate – an abiding symbol once of Germany's division and today of its unity. "Freedom is the most precious element in our political and social system," she declared in an address. "Without freedom there is no democracy. President Sarkozy spoke of "the wall of shame", while President Medvedev said: "The Iron Curtain was annihilated. We hope the era of confrontation is past." Gordon Brown told Berlin: "The whole world is proud of you – you tore down the Wall and you changed the world. Because of your courage, two Berlins are one, two Germanys are one and now two Europes are one." Hillary Clinton said, "History broke through concrete and barbed wire and signalled a new dawn."

But it took Gorbachev to remind the crowd of the single most extraordinary thing about the event they were commemorating – the fact that it was such a stunning surprise. He and the then-Chancellor Helmut Kohl knew the Wall would fall, he told the crowd, but they were ambushed by the speed at which it happened. "We were not very good clairvoyants. Every day we talked about how the German question could be solved – and then it went and happened on 9 November."

At the climax of the celebrations, Lech Walesa gave a gentle prod to a giant painted domino made of foam at the Brandenburg Gate, and, one by one, another 999 dominoes lined up from the Gate to the Potsdamer Platz in the centre of Berlin collapsed. A huge firework display followed, and the "festival of freedom" was rounded off with a concert in front of the Brandenburg Gate conducted by Daniel Barenboim, another who witnessed the events of 1989 at first hand.