Leaders from across the continent were due in the German capital to join around 100,000 revellers Monday at the Brandenburg Gate, the symbol of national unity since the peaceful revolution that tore down the Wall in 1989.
Secretary of State Hillary Clinton was flying to Berlin to give a speech late Sunday on the challenges facing the West two decades after the Cold War.
German Chancellor Angela Merkel, who will also host leaders including Russian President Dmitry Medvedev, British Prime Minister Gordon Brown and French President Nicolas Sarkozy, recalled that the end of Europe's postwar division came as an utter surprise.
"The 20th anniversary of the fall of the Wall should remind us all what incredible luck we had with the reunification of Europe and Germany," Merkel, who grew up in communist East Germany, told the Bild newspaper in an interview to be published Monday.
On the night of November 9, 1989, following weeks of pro-democracy protests, the Stalinist state's authorities suddenly opened the border.
After 28 years as prisoners of their own country, euphoric East Germans streamed to checkpoints and rushed past bewildered guards, many falling tearfully into the arms of West Germans welcoming them on the other side.
On Sunday, Germans were already out in force along the former route of the barrier which had cleaved the city in half, inspecting 1,000 giant dominos that will be toppled as part of Monday's ceremony.
Mayor Klaus Wowereit said the project, in which schoolchildren were among those to decorate the huge foam tiles, had helped underline the day's importance for those too young to remember it.
"History is palpable and alive here," he said. "The peaceful revolution of the fall of the Wall 20 years ago paved the way to an unprecedented transformation of Berlin."
In the Wall Park in the eastern district of Prenzlauer Berg, Berliners were to form a chain of handkerchiefs along the former border decorated with slogans and scenes linked to the Wall.
"Handkerchiefs are a symbol of the many tears, the farewells, the joy, the dance, the exchange between East and West," said organiser Bernd Klippel. In the run-up to the anniversary, Irish rockers U2 electrified a crowd of 10,000 at the Brandenburg Gate Thursday with a spectacular free concert that included the ballad "One", written in Berlin and partly inspired by the Wall's fall.
On Friday, artists unveiled restored murals on the longest-surviving stretch of the 155-kilometer-long (96-mile-long) Wall. Known as the East Side Gallery, the paintings were completed in 1990 and are now one of the city's biggest tourist attractions.
France was also preparing a big celebration Monday, which minister for Europe Pierre Lellouche called a gesture to make amends for misgivings about German reunification at the time the Wall fell.
A dazzling light-and-sound show will take place on the Place de la Concorde in central Paris, inspired by the impromptu concert given by Russian cellist Mstislav Rostropovich at Checkpoint Charlie two days after the Wall tumbled.
"I wanted to organise a celebration in Paris to chase away, once and for all, the fears that surrounded this period," Lellouche told Sunday's Le Parisien newspaper.