Police arrested hundreds of people who strapped themselves to the White House fence on Sunday to protest the proposed Keystone XL oil pipeline.

The protesters were mostly college students who participated in a peaceful march that began at Georgetown University and ended outside the White House. They chanted “climate justice now” and carried signs with slogans such as “don’t tarnish the earth” in an effort to persuade President Barack Obama to reject the pipeline. They say it will worsen global warming.