Dozens of world leaders walked arm in arm as they led a defiant march through Paris in the wake of the terror attacks that shocked the French capital.
Families of the victims were among over one million people who packed the city to show their support for Parisians mourning the deaths of the 17 people killed in last week's atrocities.
People on the march carried banners, placards and posters bearing all sorts of slogans of defiance.
Others carried drawings and pictures in honour of the slain cartoonists.
A huge pencil bearing the words "not afraid" was carried through the crowd, while others raised posters to create a giant image apparently depicting the eyes and glasses of the magazine's murdered editor, Stephanie Charbonnier.
Another banner bore the lyrics of John Lennon's famous song Imagine, dreaming of a world of peace.
A young boy held up a poster that read: "When I grow up, I'll be a journalist. I'm not afraid."
Similar gatherings were held in cities throughout France, with more than 600,000 estimated to have taken part in rallies outside the capital.
Rallies also took place across Europe, including London, Berlin and Dublin.
"Paris is the capital of the world today," President Francois Hollande told ministers before receiving dignitaries from around the world at the Elysee Palace.
"Nous sommes tous Francais aujourd hui" - we are all French today," said Taoiseach Enda Kenny.
He added that the demonstration of international solidarity deepened the sense of brotherhood and sisterhood between the people of France and the European Union.
"Today we march here in this city to defend that tolerance and humanity against the hatred and extremism that would dismantle and destroy them.
"In our solidarity we show the agents of such destruction that to us their actions are anathema, their propositions absurd."
Commenting on reports that Ireland is a hub for jihadist activity, he said: "I spoke to the Minister for Justice Frances Fitzgerald yesterday, and there was a meeting of the security committee. This matter is being monitored very carefully by the security authorities in Ireland," he said.
As the people gathered in Paris, waves of applause rippled out from Place de la Republique along all the roads leading to it, which were quickly gridlocked. There were few large placards but the vast majority of the crowd displayed the "Je Suis Charlie" slogan in a variety of ways, from T-shirts and stickers to face paints and hair bands.
Some 2,200 police and soldiers patrolled the city's streets to protect marchers from would-be attackers.
Police snipers could be seen on rooftops and plain-clothes detectives mingled with the crowd.
The phalanx of world leaders walking abreast yesterday were just a tiny fraction of the hundreds of thousands who participated.
Francoise Benard (69) lives near the Charlie Hebdo office in the 11th arrondissement and heard the police sirens when the killings occurred five days ago. Twelve people died.
"I grew up with Charlie Hebdo, dating back to May 1968," she said. "They really had no sacred cows, and the sad thing is that a lot of them were the last of that May '68 generation. We may not see their like again."
Naima Zouali, a 60-year-old Moroccan living in London, carried a placard saying "Marocaine. Je suis Charlie." (Moroccan. I am Charlie).
"I really felt it was important to come when I heard the news," she said. "For me, these people, it's not Islam."
Teacher Nicolas Guichet came by train from the south of Paris. He was carrying a tennis racket with a fragment of the Paul Eluard poem "Liberte" taped on both sides.
"Freedom is named Charlie," he said. "It's a movement that will bring back confidence and hope. I hope it will show a sense of community, that we can bridge divides. I'd prefer for us to win the World Cup, but it's also through an event like this that we come together."
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