Thousands of people gathered in the streets of Paris today when the negotiations on a historic climate agreement were still ongoing, unfurling long red banners to urge the world not to cross the lines that will lead to catastrophic global warming.

Organizers said more than 10,000 people participated in the rally, which came after the French government lifted a ban on protests issued after the terrorist attacks of November 13. The police stood by to make sure it proceeded peacefully. The protesters unfurled the banners starting at the Arc de Triomphe and stretching along the major boulevard Avenue de la Grande Armée. They read “It’s up to us to keep it in the ground,” and “Crime Climatique-Stop!” Thousands carried red tulips. Foghorns sounded to honor victims of climate change.

“Our communities, our climate, our survival: those are our red lines, and we’re mobilizing to defend them,” Payal Parekh, global managing director of 350.org, which helped organize the march, said in a statement. “Paris has never been an end point for us, but a chance to get an agreement that will help us continue with our fight for climate justice, If politicians won’t keep fossil fuels in the ground, we will. Our survival depends on it.”

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Activists prepare a sign in the advance of the event.

Police prepare for the demonstrators to arrive, blocking off the first 200 yards in front of the Arc de Triomphe.

Looking at their uniforms, one might think police are debating what the safe level of allowable warming ought to be. It’s just markings of different units. (Police were also donning 1C, 3C and even 4C vests.)

Using hundreds of feet of red fabric and their bodies, activists form a giant red line during the demonstration to represent the “red lines of climate safety that must not be crossed, and collectively pledge to act so that they are not.”

An activist holds up a sign reading in French “I am climate.”

Three generations of the Daulat family.

Others showed up in costume.

Activists hold anti-nuclear energy signs.

Bikers gather next to the “red line” in front of the Arc de Triomphe.

Solar energy activists.

Bill McKibben, founder of 350.org, is seen in front of the Arc de Triomphe before the start of the demonstration.

Representatives of indigenous peoples demonstrate.

Thousands of climate activists in in Paris used geo-location services on their cell phones to spell out this message to beam this message to the world on Saturday.