How Trump's wall compares to other famous walls
President Trump is vowing to go ahead with his plans to build a 3,000km wall along the border with Mexico.
It's going to stand between nine and 16 metres high and will be made of concrete.
The Republicans and their supporters say it will prevent Mexicans from illegally entering America.
There is already a fence running along the border with strict controls around people communicating between the two sides.
At one section, known as Friendship Park, where US border guards in San Diego allow people to talk through the fence to their friends and family.
There have been many walls in history built to separate nations. But how do they compare with the plans for the US-Mexico border?
Only 27 years ago the Berlin Wall was demolished
For sheer scale, let's start with the Berlin Wall.
For this we need to journey back to the 1950s when Germany was divided into east and west.
Berlin was in East Germany, the Soviet zone, but as the country's capital it was decided that it would also be divided into four areas, one controlled by each of the four countries
Residents in the American, French and British controlled west woke up one morning on August 1961 to a physical divide between them and the zone controlled by the Soviets.
At first it was just a fence but it was soon filled with concrete measuring 3.6m high in places.
It was 100km in length with an additional 66km of fencing.
Trump's wall will be long, but not the longest in history
The border between America and Mexico is around 3,000km.
So even if Trump has to detour around things like mountains he's going to have a challenge making it longer than the Great Wall of China.
The exact length of the Great Wall is hard to say but it is generally accepted that it once stood at over 20,000km long. It's visible in low Earth orbit but not from Space.
It is more than seven metres high in most places.
But Trump's wall would trump all others on height
The president can't decide how tall his wall is going to be but he has mentioned a 16-metre barrier. That would be more than three double-decker buses.
Hadrian's Wall, which Emperor Hadrian ordered in 122 AD, was just one double-decker bus in height.
It was 117km long and ran between Wallsend and Bowness, separating England from Scotland.
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