A 1906 law has been getting a lot of attention this week — the Antiquities Act, and more specifically, the provision that allows the president to set aside national monuments.

President Trump this week ordered Interior Secretary Ryan Zinke to review national monuments bigger than 100,000 acres, which were created since 1996.

We wanted to get a sense of what the Antiquities Act says, and how it came to be the law, so we called Frank McManamon. He’s the executive director of the Center for Digital Antiquity at ASU, which runs a digital repository for archaeological data. He also co-edited a book on the Antiquities Act.