BERLIN -- Massive colorful dominoes painted by German students were placed Saturday along the former path of the Berlin Wall to mark the 20th anniversary of the opening of the barrier that divided the city for nearly three decades.

Many of the upright 7.5-foot-high (2.3-meter-high) plastic foam dominoes carried messages, including "We are one people." The approximately 1,000 dominoes stretching for 1.5 kilometers (1 mile) will be toppled Monday as part of wider celebrations of the wall's fall.

One labeled "bleeding heart" showed a sword cutting through the city of Berlin, starting a crimson flow of blood speckled with crosses.

"Everyone has walls in their heads to a certain extent," said Berlin resident Stefan Schueler as he perused the domino display. "It's always a good thing if one can break them down, and I think this is a good symbol."

Former Polish leader Lech Walesa, whose pro-democracy movement Solidarity played a key role in ending communism in Eastern Europe, is to tip the first domino Monday as the artistic display comes toppling down.

U.S. Secretary of State Hillary Rodham Clinton, British Prime Minister Gordon Brown, French President Nicolas Sarkozy and Russian President Dimitry Medvedev also are expected to be on hand Monday for the formal commemorations of the wall's opening on Nov. 9, 1989.

"The fall of the wall was a very big event, and I think most Berlin residents are thankful to those who made it happen," said Berlin resident Guenter Nowak standing beside one stretch of dominoes.

German Chancellor Angela Merkel, herself a resident of East Germany when the wall fell, said in her weekly podcast Saturday that it was a day that "changed the lives of many people including me."

"It is particularly nice for us to be able to celebrate this day with our European neighbors," Merkel said. "We Germans will not forget our neighbors and allies who made the path to German reunification possible."

Researchers estimate that 136 people were killed while trying to cross the barrier during its 28-year existence.

On Saturday in a village outside Berlin, three new memorial stones were dedicated to victims of the wall.

One honored Horst Kullack, a 23-year-old who was shot by border guards on Dec. 31, 1971.

For his family, the memory is still fresh in their minds.

"He was gone, disappeared," said his father, Willi Kullack. "He did not come home. It was New Year's Eve."

He said the East German secret police came to his home the following day. He asked them where his son was.

"They said: He's not going to come anymore," Kullack recalled.