"My tour, my time on station here, happened toward the end of the Cold War but my fellow soldiers and I know that we had no idea that it was in fact close to the end", he said in a speech a few meters from where the Berlin Wall once stood.
"The values upon which Europe is founded. they are anything but self-evident".
On November 9, 1989, the East German border guards, overwhelmed by large crowds, opened the doors to West Berlin, allowing free passage for the first time since the Berlin Wall was built.
Cracks have appeared within the European Union as former eastern bloc countries like Hungary or Poland are accused by Brussels of challenging the rule of law.
That communist authorities finally opened border crossings that day "teaches us that no wall that shuts people out and limits freedom is so tall or broad that it can not be broken through", Merkel said.
"That applies to everyone in the East and West: we are stripped of any excuse and we are obliged to do our part for freedom and democracy".
Ms Merkel, who grew up in East Germany, greeted members of the public as she arrived at Bernauer Strasse where she and fellow leaders from Poland, Hungary, Slovakia and the Czech Republic placed roses at a section of the Wall left standing.More news: UEFA Europa League: Celtic face a battle in Rome
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German President Frank-Walter Steinmeier (right) welcomes Polish President Andrzej Duda in Berlin.
"In Germany, we are debating and yes, fighting, more than before, about German reunification and its consequences", he told his central European guests at lunch. The struggle of political systems had continued and the future was more uncertain than ever before, Steinmeier added.
And the differences are not just re-emerging between the former east or west blocks. Emmanuel Macron warns that now "Nato is brain dead'".
Merkel responded with uncharacteristic sharpness, calling such "sweeping judgements" unnecessary.
Back in Berlin on Friday as USA secretary of state, the day before the 30th anniversary of the Wall coming down, Pompeo had no regrets about the demise of Communist East Germany but warned that there was still authoritarianism in the world.
US Secretary of State Mike Pompeo has warned of the dangers posed by Russian Federation and China, and called on North Atlantic Treaty Organisation to grow and confront "the challenges of today".
Urging Western allies to defend hard-won freedoms, Pompeo stressed "we can never take. things for granted".