Leaders have thrown up walls and barriers throughout history \u2013 but their effects are unpredictable<\/p>\n
Four millennia ago, a Sumerian king,\u00a0his frontier beset by nomadic tribes fleeing prolonged drought in their own lands, ordered the construction of the world\u2019s first border wall: a 177km-long boundary laid in stone between the Tigris and Euphrates rivers.<\/p>\n
Since humanity\u2019s earliest city-states and kingdoms arose in ancient Mesopotamia, walls, ditches and fences have defended territory, marked the edges of empires and projected political power across the void. But the world\u2019s first border wall failed. It now lies buried beneath Iraq\u2019s desert sands. Rome\u2019s legions abandoned Hadrian\u2019s Wall long ago, and the iron curtain\u2019s razor-wire fences fell with the eastern bloc\u2019s collapse in the late 1980s.<\/p>\n
![](\"https:\/\/i.guim.co.uk\/img\/media\/f179dc34d4301d0cfecc2da831fe8798e2234eb0\/159_0_1530_1224\/master\/1530.jpg?width=140&quality=85&auto=format&fit=max&s=6519d3c65f9e01b331942977145f9f8a\" "\\"Do")
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