BERLIN (Reuters) - World leaders hailed the ordinary people who helped bring down the Berlin Wall and said the historic events of 20 years ago showed nations were capable of rising to new challenges, from terrorism to climate change.
German Chancellor Angela Merkel and leaders from Britain, France and Russia greeted tens of thousands who braved pouring rain at the Brandenburg Gate on Monday evening to celebrate the anniversary of the Wall's collapse, which paved the way for German unification and the end of the Cold War.
"Together we brought down the Iron Curtain and I am convinced this can give us the strength for the 21st century," said Merkel, who grew up in communist East Germany and crossed the Wall herself the night of November 9, 1989.
"Our good fortune obliges us to take on the challenges of our time," she added.
The grim weather did not prevent people from packing the square in front of the Gate, once a desolate no-man's land and now a powerful symbol of a reunified Germany.
Countless others watched from balconies, while some lined side streets to catch a glimpse of the leaders as they strode through the Gate from East to West, retracing the steps of Berliners who stormed the Wall 20 years ago.
French President Nicolas Sarkozy said the Wall's collapse was a call to "fight against the walls that still exist in our world and which still divide cities, regions and nations."
His Russian counterpart Dmitry Medvedev called for the building of a "new, better world" and a common battle against economic crisis, crime, terrorism and poverty.
U.S. Secretary of State Hillary Clinton urged fellow leaders to work together to advance freedom beyond "current frontiers."
After the leaders spoke, the former head of the Polish Solidarity movement, Lech Walesa, toppled the first of a chain of giant colored dominoes set up along a 1.5 km (0.9 mile) stretch where the Wall once stood.
Seconds after he knocked over the first domino, a TV cameraman crashed into him from behind. Walesa fell softly onto the domino but the cameraman tumbled hard to the wet pavement.
Backed by the Soviet Union, the East German government began erecting its "anti-fascist protection barrier" in the early hours of August 13, 1961, to end a mass flight of its citizens into capitalist West Berlin.
Initially a makeshift fence of barbed wire, it was built up into an imposing 156-km (97-mile) concrete wall ("Mauer" in German) that encircled West Berlin and was patrolled by guards with orders to shoot anyone who tried to escape.
According to a study this year, at least 136 people were killed at the Wall between 1961 and 1989 while trying to flee.
Thousands of others managed to evade the minefields, guard dogs and watchtowers, using schemes including tunnels, aerial wires and hidden compartments in cars to make it to the West.
Not a single shot was fired when the Wall fell two decades ago. That night turned into a giant city-wide party, with easterners roaming the streets of West Berlin in disbelief and residents from both sides embracing each other.
On Monday, fireworks lit up the grey sky, recreating the festive atmosphere that engulfed the city in 1989.
"I was in mother's tummy when the Wall came down," 19-year old Nika Schole said. "It's hard to imagine what people experienced that day 20 years ago, but I came here to get a feel for what it was like."
Helmut Kohl, chancellor when the Wall fell, promised easterners "flourishing landscapes" when the two Germanys unified a year later.
But despite an estimated 1.3 trillion euros ($1.9 trillion) in transfers to rebuild the East, the so-called "new states" still suffer from unemployment rates twice that of the West.
A poll of over 1,000 Germans for the Leipziger Volkszeitung daily showed one in eight wanted the Wall rebuilt -- with the numbers nearly equal in East and West.
Additional reporting by Sarah Marsh, Brian Rohan, Erik Kirschbaum and Pawel Kopczynski; Writing by Noah Barkin; editing by Mark Trevelyan