France has just lived through one of those days which will remain engraved in the national memory.
The country has known terrorism before. There were waves of Middle East-related bombings in the 1970s, 80s, and 90s. There were the Islamist murders of Mohammed Merah three years ago.
But never in half a century has there been a single attack of such cold-blooded ruthlessness. Never has there been a death toll like on the rue Nicolas-Appert.
People look on their lives rather differently when they have seen the images - not in Syria, but on the familiar streets of central Paris - of an Islamist gunman casually "finishing off" a local police officer.
The icy self-possession of the killers, their professional-looking kit, their utter disregard for "collateral" victims: it makes France feel frighteningly vulnerable.
Perhaps the most disturbing image from the amateur video is of two of the men approaching their car after the attack in order to make their getaway.
They are not running. There is no panic. They are walking.
The detail speaks volumes about the threat that France is under. These are unfamiliar killers. They are from a different world.
The other huge shock for the French is that some well-known figures are suddenly gone.
The cartoonists Wolinski and Cabu (they always go by noms de plume in the world of French bande dessiné) have been around for decades.
Their work appeared not just in Charlie Hebdo, but also in mainstream publications, like Liberation and Le Monde. Even if people did not know their names, they will have instantly recognised their styles.
It is highly symbolic that the first victims of this new era of terrorism should be icons of France's left-wing cultural consensus.
Like the newspaper they worked for, men like Cabu and Wolinski emerged in the 1960s and 70s, when it seemed axiomatic that free expression could be extended ad infinitum.
Such illusions seem almost pathetic today.
One friend of Cabu told France Info radio how shocked he was at his death, because Cabu was the "most anti-militaristic, the most gentle of creatures" - as if this was any protection against the new dread forces at large in the land.
The immediate fall-out of the attack will be expressions of national union. Already there are demonstrations in Paris and other cities.
"We are all Charlies now," they are saying.
The fact that the targets were journalists cuts deep. France takes very seriously its self-declared role of beacon to the world.
Newspapers like Charlie Hebdo are of very uneven quality - and their cartoons are often cruder than they are funny - but they carry the message that, in France, even the unsayable is still sayable.
Today, everyone can share in the common defence of French values. From the rector of Paris mosque to the National Front's Marine Le Pen, the line tonight does not vary one iota.
But how long this unity will last is another question. Soon there will be the discordant voices.
On the one hand there will be those saying the real lesson of the attack is that France should drop its "naivety" concerning Islamism in the banlieues.
There should be a much tougher line, these people will say, and the country should stop pretending it is all one happy family - barring a few aberrant individuals.
On the other side there will be those warning against what the French call l'amalgame - ie lumping all Muslims together and claiming that the problem resides somewhere within their religion.
All but eliminated
It is symbolically significant that the murders took place on the very day of the publication of the new novel by France's most respected novelist, Michel Houellebecq.
Soumission (Submission) imagines a world in which a Muslim president takes over France in 2022 and the population acquiesces.
In interviews, Houellebecq has said his theme is the end of the Enlightenment values that have prevailed in the West since the 18th century.
There can have been no clearer product of those Enlightenment values than Charlie Hebdo. Voltaire was their inspiration.
This evening Charlie Hebdo has been all but eliminated. Its leading men and women are dead.