As Berliners watch 8,000 balloons being released into the night sky this evening, old divisions between east and west will symbolically vanish into thin air with them. Yet the runup to the festivities has already served up plenty of reminders that, 25 years after the fall of the wall that divided the city for three decades, the scars of history are hurting more than ever.

Speaking at a symposium near the Brandenburg Gate yesterday morning, former Soviet president Mikhail Gorbachev warned that the world was “on the brink of a new cold war” and strongly criticised the west for having sown the seeds of the current crisis by mishandling the fallout from the collapse of the iron curtain.

“Instead of building new mechanisms and institutions of European security and pursuing a major demilitarisation of European politics … the west, and particularly the United States, declared victory in the cold war,” said the man behind the Soviet Union’s glasnost and perestroika reforms.

“Euphoria and triumphalism went to the heads of western leaders. Taking advantage of Russia’s weakening and the lack of a counterweight, they claimed monopoly leadership and domination in the world.”

The enlargement of Nato, Kosovo, missile defence plans and wars in the Middle East had led to a “collapse of trust”, said Gorbachev, now 83. “To put it metaphorically, a blister has now turned into a bloody, festering wound.”

Previously an outspoken critic of Vladimir Putin, Gorbachev backed the current Russian president’s stance over Ukraine, urging western leaders to “consider carefully” Putin’s recent remarks at the Valdai forum : “Despite the harshness of his criticism of the west, and of the United States in particular, I see in his speech a desire to find a way to lower tensions and ultimately to build a new basis for partnership.”

Such strong words of criticism, voiced by the man still affectionately known as “Gorbi” to many in Germany, came at the end of a week which has seen the value of the rouble tumbling dramatically as a result of western sanctions.

Friday afternoon had seen another reminder of the old east-west tensions still running through Germany when the usually rather staid proceedings of the Bundestag were shaken up by a musical guest performance. Veteran songwriter Wolf Biermann, who was kicked out of the GDR in 1976, performed a protest song called Ermutigung (Encouragement) and took a number of swipes at politicians from Die Linke (the Left party), successors to East Germany’s ruling party, the SED.

“Your punishment is to have to listen to me here – enjoy”, Biermann said, while gesturing towards the leftwing parliamentarians. He went on to describe Die Linke MPs as “dragon spawn” and “the miserable dregs of something that had luckily been overcome”.

Only last week German president Joachim Gauck, a former head of the Stasi archives, had questioned whether the Left party had “really distanced itself from the ideas the SED once had about repression of people”. Die Linke is on the verge of gaining its first state premier, in the Thuringia region, something Gauck said “people of my age who lived through the GDR find quite hard to accept”.

At the very least, such score-settling should stop this weekend’s festivities, taking place under the motto “courage for freedom”, from turning into a merely nostalgic affair. Events in Berlin will mark the culmination of a remarkable chain of events which resulted in the opening of border checkpoints in Berlin on the night of 9 November 1989. At least 138 people died trying to cross the inner-German border in the capital, more than 1,000 in the country as a whole, in the postwar years.

A host of historic key players and celebrities have already dodged a nationwide train strike in Germany to descend on the capital. Yesterday evening German chancellor Angela Merkel, who grew up in East Germany, attended a memorial concert at the Berliner Ensemble, the theatre founded by the playwright Bertolt Brecht.

On Sunday, Merkel will open a new exhibition centre at Bernauer Strasse, near the Bornholmer Strasse checkpoint where the then 35-year-old chancellor crossed over to the west for the first time. “I think you never forget how you felt that day – at least I will never forget it,” the chancellor said in a recent podcast. “I had to wait 35 years for that feeling of liberty. It changed my life.”

At least two million people are expected to attend a grand street festival at the Brandenburg Gate. The former Polish president Lech Walesa, Hungarian ex-president Miklos Nemeth, as well as Gorbachev and German president Gauck, are all expected to take to the stage.

Music will be provided by the Berlin State Orchestra, conducted by Daniel Barenboim, as well as East Berlin rock band Silly and British singer-songwriter Peter Gabriel, performing David Bowie’s Heroes.

The centrepiece of the festivities will be formed by an ambitious art installation. Since Friday morning, 8,000 white balloons have been pegged to the ground along the former border. After sunset, they light up to form a 15km-long “wall of light”. This evening the balloons will be released into the air one by one, to the music of Beethoven’s Ode to Joy.

Berlin mayor Klaus Wowereit, as well as guests of honour including Nobel peace prize winner Muhammad Yunus, Nasa astronaut Ron Garan and Wikipedia founder Jimmy Wales, will start the balloon release at 7pm local time.