Government contractors have begun to build prototypes of US President Donald Trump’s proposed border wall with Mexico.
Bidding documents confirm that four of the eight prototypes are to be solid concrete and four are to be made of “other materials”.
Last week Trump said that the wall should be see-through, to curb the flow of drugs that are entering the US from Mexico.
Roy Villarreal, acting chief of the Border Patrol's San Diego sector, told reporters another contractor will evaluate each model, which will be up to 30ft (nine metres) high and 30ft long.
The concrete designs will have openings to allow agents to see across the border.
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