President Donald Trump has set in motion his plan to build an “impenetrable, physical, tall, powerful, beautiful, southern border wall” between the US and Mexico.
The border is about 1,900 miles (3,100 km) long and traverses all sorts of terrain.
Mr Trump says his wall will cover 1,000 miles and natural obstacles will take care of the rest.
But how much will it cost and who is going to foot the bill?
What is the estimated budget?
“I would build a great wall, and nobody builds walls better than me, believe me, and I build them very inexpensively.”
Mr Trump claims the total cost of the wall will be $10bn (£7.5bn) to $12bn. But estimates from fact checkers and engineers seem to be universally higher.
Senate Majority Leader Mitch McConnell estimated it will cost between $12-15bn, as he addressed reporters at a Republican conference in Philadelphia.
The 650 miles of fencing already put up has cost the government more than $7bn, and none of it could be described, even charitably, as impenetrable, physical, tall, powerful or beautiful.
There are other reasons the costs would be likely to escalate beyond Mr Trump’s price tag – his plans require extending the wall into increasingly remote and mountainous regions, raising the building costs substantially.
Donald Trump has been very vocal about keeping illegal immigrants out of the United States, with plans to build a border wall along the U.S./Mexico border when he takes office. Do you support this plan?