By Adam Easton
BBC News, Gdansk
Some marked the day with flowers at Gdansk shipyard
It might not have been a public holiday - but it was a national day of celebration in Poland.
Gdansk, the home of the Solidarity movement, was particularly festive.
Thousands of people crammed into Solidarity Square beside the main gate of the shipyard to commemorate the 25th anniversary of the birth of the movement.
Crowds filled the streets leading to the square. Among them were pensioners, families with children's strollers and scouts.
Many wore armbands in the national colours of red and white. Others brought flags with Solidarity written in its famous red letters.
Under a clear blue sky they listened to an open-air Mass led by Pope John Paul II's former private secretary, Archbishop Stanislaw Dziwisz.
The overwhelming majority of Poles look to the Roman Catholic Church for moral and spiritual guidance. And under communism, the Church was one of the few places they could go to hear the truth.
The Church and in particular the Polish pope, played a vital role in galvanizing support for Solidarity.
Above the huge stage in the square a banner quoted John Paul II.
It read: "Solidarity opened the gates to freedom."
'Beginning of end'
Thirty world leaders joined the crowds at the Mass.
Among them were the presidents of Germany, Ukraine and the European Union. Also present were the UK Deputy Prime Minister John Prescott and former US Secretary of State James Baker.
Earlier, the leaders paid tribute to Solidarity at an international conference across town.
The President of the European Commission, Jose Manuel Barroso, was applauded when he repeated the strikers' slogan: "Without Solidarity there is no freedom".
Lech Walesa, the leader of the Gdansk strike in August 1980, received a standing ovation. He said Solidarity had started the process which destroyed the old order when the world was divided into two camps.
Historian Timothy Garton Ash, who was in Gdansk for the strike in 1980 said: "With hindsight we can see it was the beginning of the end of communism in Europe and the Cold War."
Within months of its founding in 1980, the Solidarity trade union became a national political movement with 10 million members.
It was a threat the communist authorities could not bear, and in December 1981 they declared martial law and jailed its leaders.
But under Mr Walesa's leadership, Solidarity survived underground and went on to negotiate the end of communism in Poland in 1989.
But there was some dissent in the city amid the celebrations.
A small group of present-day Solidarity trade union members protested inside the shipyard against the official ceremonies.
Above its historic main gate they posted their demands for greater social justice, just as the original strikers had done in 1980. A banner they put up read: "The Gdansk shipyard has been robbed and destroyed, although it celebrates today."
The transformation to capitalism has often been painful here.
Under communism, unemployment officially did not exist. Now it stands at 18%, the highest rate in the EU.
After the shipyard went bankrupt and sold several years ago, the workforce has shrunk from over 20,000 to just 3,000.
But today, most minds were concentrated on Solidarity's historic achievement.
"I think Solidarity greatly changed history - especially here in this part of Europe," said 30-year-old scientist Stanislawa.
"It was the first step to finish communism. So for me it is very important."