The U.S. Border Patrol said workers were installing steel rebar at a site south of Donna, a small city in South Texas’ Rio Grande Valley.
The rebar will reinforce concrete panels that will in turn be topped with 18-foot (5.5-meter) steel bollards. Crews will also clear vegetation 150 feet (45 meters) in front of the wall.
Environmental advocates and opponents of the wall have warned that construction will destroy critical habitat and require the seizure of land from potentially hundreds of people in South Texas.
The Border Patrol says a wall will deter drug and human smuggling. The ongoing construction was funded by Congress last year.