The US government has announced the start of construction on eight prototype barriers for the border with Mexico, a campaign promise of President Donald Trump.
The Customs and Border Protection says four of the prototypes will be made from concrete, while the others are from “alternate or other materials”.
Its plan is to try out several sections of wall near San Diego.
Mr Trump had promised to build a “big beautiful wall” between the countries.
With a heavy federal and local law enforcement presence, workers have broken ground in an area surrounded by chain link fencing at Otay Mesa, one of three ports of entry in the San Diego-Tijuana metropolitan region.
The prototypes will be up to 30ft (9m) high and 30ft long and are expected to be completed within 30 days.