Massive crowds gathered in and around Place de la République in central Paris to express solidarity with those killed at a satirical weekly newspaper and at a Jewish supermarket last week.
An estimated two million demonstrators were also there to support freedom of expression in the wake of the horrific attack on Charlie Hebdo on January 7. It was followed by the shooting of a police officer in southern Paris and the death of four hostages at the Hyper Cacher kosher grocery outlet in the eastern part of the city.
The three gunmen who perpetrated the attacks were all killed by police.
Most of the marchers went from the square down Boulevard Voltaire to Place de la Nation in eastern Paris. Others took an alternate route.
They walked not far from the offices of Charlie Hebdo, where 12 people were murdered. The victims included eight newspaper staff members, a visitor, a maintenance person, a police bodyguard assigned to protect editor Stephane Charbonnier, and a Muslim police officer standing on guard outside the building.
Al-Qaeda in the Arabian Peninsula claimed responsibility for the attack on the weekly paper, saying it sought vengeance for cartoons of the Prophet Mohammed.
Today's unity march attracted leaders from many religious faiths, including Islam. In addition, heads of state and senior officials from more than 40 countries joined French president Francois Hollande at the event. Among them was German chancellor Angela Merkel, British prime minister David Cameron, and Israeli prime minister Benjamin Netanyahu.
Public Safety Minister Steven Blaney was there representing Canada. U.S. attorney general Eric Holder is in Paris attending talks on security issues, but was not seen among the world leaders during the march.
Meanwhile, the leader of France's anti-immigration National Front party, Marine Le Pen, was not invited. Former French prime minister Nicolas Sarkozy, however, was part of the procession.