Tens of thousands rallied on Washington’s National Mall on Sunday for what organizers dubbed the largest climate rally in U.S. history. The “Forward on Climate” event was held to urge President Obama to reject the controversial Keystone XL oil pipeline and commit the U.S. to binding limits on emissions of greenhouse gases. Indigenous leaders Chief Jacqueline Thomas of the Saik’uz First Nation and Casey Camp of the Ponca Nation of Oklahoma said the Keystone pipeline endangers their communities.

Chief Jacqueline Thomas: “It puts at risk my neighbors to the east of me that live at the tar sands. The government doesn’t recognize these people, and these people have been dying of mysterious cancers. Their water is polluted. Their animals are sick. And Mother Earth is sick.”

Casey Camp: “And we’re here to make a difference. We’re here to be in solidarity with all of us who understand that we have a very slim opportunity to make human life continue to exist. And that’s our choice.”

Groups opposing coal production, nuclear power and hydraulic fracturing for natural gas participated in the protest, as did a number of interfaith organizations. Several smaller parallel rallies were held in cities across the country.