BERLIN - Germany on Saturday marked the 30th anniversary of the fall of the Berlin Wall that separated East and West Germany, with President Frank-Walter Steinmeier thanking Eastern European neighbors for enabling a peaceful revolution.The toppling of the wall, which had divided the Communist-ruled East and the capitalist West in Berlin for nearly three decades and became a potent symbol of the Cold War, was followed a year later by the reunification of Germany in 1990. "Together with our friends, we remember with deep gratitude the events 30 years ago," Steinmeier said during a ceremony at the Bernauer Strasse Berlin Wall Memorial, which was also attended by Chancellor Angela Merkel and heads of state from Poland, Hungary, Slovakia and the Czech Republic."Without the courage and the will to freedom of the Poles and Hungarians, the Czechs and Slovaks, the peaceful revolutions in Eastern Europe and Germany's reunification would not have been possible," Steinmeier said.During the ceremony, Steinmeier and the presidents of Poland, Hungary, Slovakia and the Czech Republic placed roses in a small gap in the remains of the wall at the memorial.In August 1989, Hungarian border guards for the first time allowed people from East Germany to cross freely into Austria, paving the way for the fall of the Berlin Wall three months later and with it the end of the Iron Curtain.Steinmeier pointed out, however, that the historic event did not mark the "end of history" as U.S. historian Francis Fukuyama stated. The struggle of political systems had continued and the future was more uncertain than ever before, he added."Liberal democracy is being challenged and questioned," Steinmeier said. That's why Germany and its European allies had to fight every day for a peaceful and united Europe with each country having to do its part to overcome differences, he added.His message was echoed by Merkel in a brief speech during a commemorative service at the memorial's chapel."The values on which Europe is founded -- freedom, democracy, equality, the rule of law, respect for human rights -- are anything but self-evident. And they have to be filled with live and must be defended again and again," she said.The festivities in Berlin were due to culminate with a party at the Brandenburg Gate in the evening featuring the Staatskapelle Berlin orchestra directed by Daniel Barenboim and electronic music with techno DJ legend WestBam.