The key countries in the Cold War pledged yesterday to fight division and meet the new challenges of the 21st century as Europe marked the 20th anniversary of the fall of the Berlin Wall

In emotional addresses delivered at Berlin's Brandenburg Gate, the leaders of the United States, Russia and Britain joined German Chancellor Angela Merkel, Mikhail Gorbachev, Lech Walesa and envoys from across the 27-nation European Union in saluting the event that changed history.

A crowd of more than 100,000 came to the "Festival of Freedom", featuring concerts by the city's classical orchestra and Bon Jovi and saw the toppling of a thousand giant dominoes symbolising the end of Berlin's 28-year division.

Walesa, the Nobel Prize-winning Polish trade unionist who in the early 1980s delivered the first crushing blows against the Iron Curtain, had the honour of pushing over the first of the styrofoam dominoes.

As the last one fell, the crowd chanted "F - R - E - I - H - E - I - T", the letters for "freedom", and the fireworks began to soar.

"Twenty years ago the door to freedom opened up and a seemingly invincible wall that divided a people and an entire continent suddenly became permeable," declared Merkel.

"Our good fortune obliges us to take on the challenges of our time ... freedom and security in the world, the strengthening of growth, wellbeing and justice, the protection of the environment and our natural resources, and the defence of human rights all over the world."

US President Barack Obama, in a surprise video message, said November 9, 1989, would always be a cherished date in the United States. "This anniversary is a reminder that human destiny will be what we make of it. Even in the face of tyranny, people insisted that the world could change."

US Secretary of State Hillary Clinton said: "A physical wall, may have come down but there are other walls that exist that we have to overcome."

French President Nicolas Sarkozy described the fall of the wall as "a call to fight oppression and to tear down all the walls that still separate the world, that divide cities, regions and nations".

"This is the message that a unified Europe proudly embodies and delivers to the world," he said.

British Prime Minister Gordon Brown said the destruction of the seemingly impregnable wall, leading to Europe's reunification, demonstrated the power of will.

"What seems impossible - an end to nuclear proliferation, an end to extreme poverty, an end to climate catastrophe - can become possible and be unstoppable, thanks to the power of people united in common endeavour."

The Russian President, Dmitry Medvedev, said: "Confrontation is in the past. Today we want to build a different, new, better world." But, in a jab at the United States, he said that the world had to be "multipolar".

The Brandenburg Gate, a triumphal arch, was the focal point of the 3.5-metre-high, 155km wall and steel fence that the communist-run German Democratic Republic built around West Berlin in August 1961.

The edifice was coupled with fortifications that ran for 1400km along the inter-German border, ostensibly an "anti-fascist barrier" but in reality a barricade to stop the oppressed population of East Germany heading west.

At least 136 people were killed as they tried to cross to West Berlin, running the gauntlet of a "death strip" guarded by watchtowers, barbed wire, tripwire-activated machine guns and troops with shoot-to-kill orders.

On the night of November 9, the embattled East German regime, abandoned by Soviet leader Gorbachev, announced it was relaxing travel restrictions.

In scenes of confusion, tens ofthousands of East Germans streamed to West Berlin, where they were greeted with tears of joy, garlanded with flowers and their smokyTrabant cars showered with sparkling wine.

The 20th anniversary began soberly, with a memorial service for those who died trying to gain freedom.

It was held in an east Berlin church that became a focal point of democratic activism in the northern autumn of 1989, shaking the Stalinist regime.

Merkel, flanked by Gorbachev and Walesa, then walked through the former Bornholmer Strasse crossing point and into the former Western sector. It was a moment that reflected the odyssey of both Merkel andGermany.

On the November 9, 1989, Merkel walked across Bornholmer Strasse as one of the stunned, tear-stained throng of East Germans. Yesterday she took the same route, but this time as the first eastern Chancellor of post-unification Germany.

Paris organised its own tribute with a sound-and-light show at the Place de la Concorde, where 27 cellists played on top of plinths representing fragments of the wall.

It was inspired by the impromptu concert given at Checkpoint Charlie, one of the Cold War flashpoints, by Soviet cellist Mstislav Rostropovich on November 11, 1989.