dividing walls:
The latest wall to divide city neighborhoods went up in Baghdad in April, built by American soldiers using 12-foot (3.7-metre) high grey concrete slabs weighing more than six metric tons each. The 3-mile-long construction separates a Sunni Muslim district from a Shi’ite area. It provoked protests from both communities and Shi’ite cleric Moqtada al-Sadr termed it “racist.”
(...) Many of the ruses used when the Iron Curtain was still up — hollowed out hiding spaces in cars, tunnels, hook ladders — are still used now. Then, successful crossers were hailed as heroes of freedom. Now they are seen as a threat or a burden.
(...) That applies to one of the least known but longest border barriers of modern times, built by Morocco in the 1980s to curb attacks by the Western Sahara independent movement, Polisario, on territory it claims for itself. It lies behind a set of walls some 1,700 miles long and 10 feet high made of earth, rock and sand built in the 1980s. The wall is defended by thousands of Moroccan troops and fortified by bunkers and fences, barbed wire and landmines — between 200,000 and several million of them, depending on who does the estimating.
(...) Saudi Arabia has quietly invited bids for a 550-mile high-tech fence — complete with sensors, night vision cameras, face-recognition software, barbed wire — to seal off its border with Iraq.
(...) Almost invariably, governments that decide on physical separation from a neighbor predict that it would reduce tension but, at times, that remains wishful thinking. In April, for example, a firefight broke out between Afghan and Pakistani troops after the Afghans tried to tear down parts of a fence running through a tribal area. Pakistan started building a fence along part of the 1,500-mile (2,500-kilometer) border under U.S. pressure to close the routes of Taliban fighters heading to Afghanistan to join the war against U.S. and multinational forces.
(...) But Spain has built double fences 10 to 20 feet high and topped with razor wire around its wealthy enclaves of Ceuta and Melilla in Morocco to keep immigrants out.
(...) The fences have had an effect similar to the walls on the border between the United States and Mexico: would-be immigrants from poor countries looked for other ways to reach a rich country. Stepped-up Spanish coastal patrols and better radar systems prompted African migrants to make riskier voyages to the Spanish-owned Canary Islands. Hundreds have drowned.
(...) If history is a guide, no border fortification can seal off a country entirely. Even the mother of all walls, the Great Wall of China, at around 4,000 miles the longest border wall ever built, failed to keep out the northern barbarians against whom it was meant to protect.