In the capital, many bowed their heads under umbrellas earlier as the bells of Notre Dame Cathedral tolled across the city.
It was a scene mirrored in towns and cities across France, and elsewhere in Europe, as people honored those who paid with their lives for press freedom.
At Place de la Republique, where Parisians have been gathering for vigils, Pierre Cornet Thursday night held a spray-painted sign with a message in English: "We are Charlie."
"We are (determined) that they don't have the last word," he said of the terrorists. "We have to win, and we will win ... because our struggle is liberty."
Waving a sign with the now familiar "I am Charlie" refrain, Lesley Martin sounded defiant.
"I am not afraid," she said. "Tonight I'm here and, if tomorrow I have to be here, I don't care if anybody comes and just wants to do something really bad here. I'm not afraid to die."
Earlier, Journalist Isabelle Bordes, who works for regional newspaper Ouest France, was one of those who felt they had to observe the vigil in Paris despite pouring rain.
"We are here for Charlie, for the journalists who died yesterday, but also for the journalists who are alive and will go on," she said.
"We need Charlie -- it is unbearable to think that a newspaper could be killed by weapons -- so there will be another issue next week."
She said the attack had left her feeling the same way that September 11
did. "I feel like there will be a 'before' and an 'after.' I just hope everyone will be aware of their responsibilities: We must be critical but human; we have to be careful with words, with images; we have to be precise when we talk about facts."
Bordes said she had been impressed and touched by the scale of protests against the attack, even in her village, Granville in Normandy.
"There are only 13,000 people, and 400 demonstrated. I am very proud of my little town. There is a great photo of an elderly man with a long white beard and an 'I am Charlie' sign, who keeps crossing the road (to disrupt the traffic)."
Myky Mylan lit incense at the vigil site.
"Liberty is an everyday struggle," she said. "It's a shame that we had to wait for a drama like this before taking action. ... We need a slap in the face to react, but at least it makes a reaction. Hopefully, it will be a positive one with long-term effects."
Kelland Hutchence, originally from Cardiff, Wales, but now living in France, said he and his French partner came to pay tribute by laying flowers at a Paris vigil site. Hutchence also put up a sign saying "I am Charlie" in Welsh.
"We were terribly upset by what happened, and very touched by the response to this horrible, disgusting event. I hope very much that it will not affect people's view of decent Muslim people. I think that's what they want to do, to foment a religious war against Islam, but I hope that there is no reaction, that people don't take reprisals."
As the initial shock wore off Wednesday, the grand boulevards in most of France's major cities became scenes of mourning and solemn demonstrations, with crowds declaring themselves unbowed by the gunmen
's assault on Charlie Hebdo's
offices. Four of its cartoonists were among those killed in the gunfire.
Marchers raised pens skyward. They lit candles in the dark. They wrote "liberty" and "free expression" on placards in rallies, as they took to the streets only hours after the deadly attack.
"The world has become so sick that (being a humorist or cartoonist) has become a dangerous profession!" said a poster carried by one woman in a mass of protesters in Paris' Place de la Republique.
One mourner, Corentin Vacheret, described the slain cartoonists as journalists who "are famous in France, especially among people who value the liberty of expression."
"The fact that they were killed in the most insane circumstances is just sickening," Vacheret said. "I am not a fan of big protests, but I wanted to express that we are not afraid, that this is not going to make us renounce our liberty of expression."
Rallies also unfolded Wednesday night in Tours, Toulouse, Brest, Lyon, Rennes and Poitiers, among other cities in France, long regarded as a cradle of democracy and liberty. They were joined by demonstrations elsewhere in Europe, including London, Barcelona, Berlin and Rome.
The most immediate rallying cry against the attack was "Je Suis Charlie," or "I Am Charlie," in reference to the weekly satirical magazine's title, Charlie Hebdo.
Another sign at the rally in Place de la Republique declared: "I stand up and I express myself with words because they are still the most beautiful weapon!"
According to Le Monde newspaper, French police said as many as 15,000 people gathered in the Place de la Republique, which was closed to traffic.
Demonstrators' candles glowed in the darkness. Marchers were mostly silent for the first hour, Le Monde reporter Maxime Goldbaum tweeted, but then began chanting, "Charlie! Charlie! Charlie!" and "We are Charlie!"
At another point, the chant became a play on words: "Charlie-Charlie-Charliberte!"
One student held a sign at the Paris rally saying, "Long live liberty! Long live France! Long live Charlie!"
Just a few feet away from the main demonstration, the gathering took a more somber tone. Dozens of people created a shrine of pens and pencils on the paving stones, encircled by tea lights and candles.
Many visitors -- some in tears -- stood or sat quietly, with heads bowed, appearing as if they were trying to understand what happened in an office a few streets away.
Faycal Haddad, a Muslim, carried a homemade sign stating "not in my name, not in the name of my religion."
"I don't want anyone to say that my kids, someone from my family, is involved -- this is not Islam," Haddad said. "If I thought that this was what Islam was about, I would not be part of it. No religion in the world can authorize anyone to kill.
"We need to unite against these few people, they are a bacteria, a virus, and we need to find a solution," Haddad added.
Emmanuel Leger brought his son Binhkim, 15, to a vigil where both held burning candles.
"I think today is the day everything changed," the father said.
In London, about 700 people gathered at Trafalgar Square in an evening vigil for the French victims.
Many condemned the attackers.
"Shame on you. Pens versus gun? There's no competition, is there. Shame on you, shame on you," said one man attending the London event. "It's the most cowardly thing you can do."