A world of walls is a series of the Brazilian newspaper Folha de S. Paulo on barriers built to close borders, stop migrants or hide poverty. A more and more interconnected world is raising walls and fences to keep out those it considers undesirable. The number of physical barriers that existed in 2001 was 17: the figure has presently jumped up to 70.
Some of them reinforce borders. Others divide the same population. Some seek to stop the refugee flow. Others hide poverty. Or fear. Or war. Or inequality. Or climate change.
Folha went to four different continents to uncover what - and who - lies behind them.