Now, according to US Customs and Border Protection (CBP) in its 6 October status report, the southern border has 669 miles of "primary barrier" - the first structure people heading from Mexico to the US will encounter - and 65 miles of "secondary barrier" - which usually runs behind the primary structure as a further obstacle.

This means that in areas where no barricades existed before, they have built 15 miles of new, primary barrier or "border wall system", as it is called by CBP.

​​About a further 350 miles of barrier has been built, according to CBP, made up of replacement structures and some new secondary barrier.

Throughout his 2016 election campaign, when he described it, he talked about concrete.

But once elected, he began referring to a barrier made of steel, which would enable border agents to see through it.

And what has been built so far is mostly such steel fencing.

The latest figures suggest the number of migrants apprehended at the southern border this year have fallen after doubling between 2018 and 2019.

While the majority of the heroin in the US does come from Mexico, the Drug Enforcement Administration says most of it is hidden in privately owned vehicles or transporter lorries, mixed with other goods, and smuggled through legal entry points.