As migrants try to find alternative routes into Europe, governments are looking at how to seal their country's borders more effectively.

Fences and walls have been erected at key crossing points around the world.

In the US, Republican presidential candidate Donald Trump is calling for a "wall" to be built along the entire southern border with Mexico.

The BBC looked at where the fences are designed to keep out undocumented immigrants.

Video journalists: Andrew Webb and Olivia Lace-Evans

Graphics: Nick Davey