Rio says the walls are needed to protect its forests from the spread of favelas
On the 20th anniversary of the fall of the Berlin Wall, BBC Mundo looks at barriers which are still standing - or have gone up since - around the world.
Since the beginning of the year, Rio de Janeiro has been building walls around some of its favelas, the shanty towns that crowd the hills around the city.
In total, 13 favelas will eventually be surrounded by concrete with a total length of 14km (8.6 miles) and a height varying between 80cm (32 inches) and 3m.
The aim is to prevent the precariously-constructed communities spilling over into the forest and destroying the surrounding vegetation of the Tijuca Park, one of the largest urban nature reservations in the world.
Officials say the Atlantic forests in the region have already lost an estimated 90% of their surface area.
In Santa Marta district, 600m of wall has already been erected, while in Rocinha the government has reached an agreement with the 200,000 residents to limit the wall to those areas at risk of landslides.
The rest will be made up of ecological paths and parks.
Some critics think Rio's walls are an attempt to separate the poor areas from the richer ones situated between the favelas and the sea.
Others say they are intended to limit drug trafficking, as part of a planned regional government clamp down.