Contractors have begun building eight prototypes of US President Donald Trump's proposed border wall with Mexico.
The building process will last about 30 days, Customs and Border Protection said.
Each prototype will be up to nine metres high and nine metres long.
Bidding documents say four of the prototypes are to be solid concrete and four are to be made of "other materials".
Mr Trump said on Friday that the wall should be see-through, appearing to cast doubt on the concrete designs.
Funding to extend the wall beyond its distance of 1,046 kilometres is in doubt.
Democrats have balked at Trump's $2 billion request to replace 22 kilometres in San Diego and build 96 kilometres in Texas' Rio Grande Valley, the busiest corridor for illegal crossings.