Mani Albrecht/U.S. Customs and Border Protection

Ground views of different border wall prototypes as part of the Wall Prototype Construction Project near the Otay Mesa Port of Entry in October 2017.

Six companies have built eight prototypes for a border wall near San Diego.

The wall was, of course, one of President Donald Trump’s signature pledges on the campaign trail.

Reece Jones has studied border walls.

He’s a professor of geography at the University of Hawaii and author of the book, "Violent Borders: Refugees and the Right to Move."