BERLIN - As crowds cheered, 1,000 colorful mammoth dominoes marking the path where the Berlin Wall once stood were toppled yesterday, symbolizing both the moment 20 years ago that the wall came down and the resulting fall of communist countries in Eastern Europe.

It was the finale to a day of memorial services, speeches, and events that attracted leaders from around the world, including former Soviet President Mikhail S. Gorbachev.

Angela Merkel - Germany's first chancellor to be raised in the former communist east - and Gorbachev stood shoulder to shoulder as they crossed a former fortified border-crossing point between East and West Berlin to cheers of "Gorby! Gorby!"

"Looking back, we can see many causes that led to the peaceful revolution, but it still remains a miracle," German President Horst Koehler told the leaders of all 27 European Union countries, Russian President Dmitry A. Medvedev, and Secretary of State Hillary Rodham Clinton.

Merkel called the events of Nov. 9, 1989, an "epic" moment in history. "It was one of the happiest moments of my life," she told the tens of thousands of people packed around the Brandenburg Gate.

In a video message screened at the main event, President Obama paid tribute to the dissidents and demonstrators who ushered in the wall's demise.

"Let us never forget Nov. 9, 1989, nor the sacrifices that made it possible," Obama said to applause and cheers.

Clinton paid tribute to Germany and other countries that shook loose communist binds.

"We remember the people of the Baltics who joined hands across their land. ... We remember the students of Prague who propelled a dissident playwright from a jail cell to the presidency," Clinton said. "And tonight we remember the Germans, and especially the Germans in the East who stood up to say, 'No more.' "

Merkel also recalled the tragic side of Nov. 9 for Germans: the Nazis' Kristallnacht, or Night of Broken Glass - an anti-Semitic pogrom 71 years ago. At least 91 German Jews were killed, hundreds of synagogues destroyed, and thousands of Jewish businesses vandalized and looted in the state-sanctioned riots that night in 1938.

"Both show that freedom is not self-evident," Merkel said. "Freedom must be fought for. Freedom must be defended time and again."

Uwe Kross, 65, a retiree, fought back tears as he recalled watching the 1989 drama unfold, hours after a confused announcement had come that East Germany was lifting travel restrictions.

"That night, you couldn't stop people," Kross said. "They lifted the barrier and everyone poured through.. . . Normally it was very quiet up here, but that night we could hear the footsteps of those crossing, tap, tap, tap."

Merkel, one of thousands to cross that night, recalled that "before the joy of freedom came, many people suffered."

She lauded Gorbachev, 78, with whom she shared an umbrella yesterday amid a crush of hundreds, eager for a glimpse of the man many still consider a hero for his role in pushing reform in the Soviet Union. "You made this possible," she said.

Later, Merkel also thanked Germany's neighbors to the East. She welcomed several leaders who dared to stand up for democracy, including Poland's 1980s pro-democracy leader, Lech Walesa, and Miklos Nemeth, Hungary's last prime minister before communism collapsed. The two men pushed the first domino.

Music from Bon Jovi and Beethoven recalled the joy of the border's opening, which led to German reunification less than a year later and the swift demolition, after nearly three decades, of most of the 96-mile wall.