BERLIN — Ulrich Sauff and his wife stared at the mammoth domino pieces marking the path where the Berlin Wall once stood and reminisced about life in the barrier's shadow.

"It was like a prison," said Sauff, 73, who lived on the western side of the wall. "For us 'Wessis,' the few kilometers from our old home to our new home (in the East) was unthinkable."

The Sauffs were among those who gathered Monday to celebrate 20 years of unity, marking the day the wall came down. Thousands cheered as 1,000 colorfully decorated dominoes along a mile-long route were toppled to symbolize both the moment the wall came crashing down and the resulting fall of communist governments 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 leader Mikhail Gorbachev.

Chancellor Angela Merkel and 78-year-old 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 Medvedev and Secretary of State Hillary Rodham Clinton.

Merkel — Germany's first chancellor to be raised in the former communist East — called the events of Nov. 9, 1989, an "epic" moment in history.

"For me, it was one of the happiest moments of my life," Merkel told a crowd of tens of thousands packed around the Brandenburg Gate.

In a video message screened at the main event, President Barack Obama paid tribute to the dissidents and demonstrators who ushered in the fall of the wall 20 years ago.

"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 who shook loose communist bonds.

"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," she 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.