Indian Border Security Force (BSF) personnel symbolically slam gates shut as they perform during the daily beating of the retreat ceremony on the India-Pakistan Border at Wagah on February 20, 2017. All pics/AFP

Afghanistan-Pakistan border: This photograph taken on February 9, 2017, Afghan nationals wait to cross the border between Pakistan and Afghanistan at the Torkham Border Post in Pakistan's Khyber Agency

Afghanistan-Pakistan border: This photograph taken on February 9, 2017, Afghan nationals wait to cross the border between Pakistan and Afghanistan at the Torkham Border Post in Pakistan's Khyber Agency

France-Britain border: A photo taken on February 2, 2017 in Calais, shows a four-metre-high (13-foot) wall, running along a kilometre-long stretch of the main road leading to Calais port, aimed at stopping migrants who attempt to reach its shores. The wall was built to boost a network of wire fences that had failed to prevent near nightly attempts by migrants to waylay trucks en route to Europe's second-busiest port. Calais has for years been a staging post for attempts by migrants to sneak into Britain by stowing away on trucks or trains crossing the Channel

France-Britain border: A photo taken on February 2, 2017 in Calais, shows a four-metre-high (13-foot) wall, running along a kilometre-long stretch of the main road leading to Calais port, aimed at stopping migrants who attempt to reach its shores. The wall was built to boost a network of wire fences that had failed to prevent near nightly attempts by migrants to waylay trucks en route to Europe's second-busiest port. Calais has for years been a staging post for attempts by migrants to sneak into Britain by stowing away on trucks or trains crossing the Channel

An Armoured Personnel Carrier (APC) patrols along Macedonia's southern border with Greece that has served as European border for refugees in Gevgelija on February 18, 2017

An Armoured Personnel Carrier (APC) patrols along Macedonia's southern border with Greece that has served as European border for refugees in Gevgelija on February 18, 2017

Greece-Turkey border: A pocket-sized section of a 12 kilometer-long planed fence that Greece is planning to build along its northeastern border with Turkey to keep out illegal immigrants is seen outside the village of Kastanies at the Greek-Turkish border on April 11, 2012. The 2 meter-long stretch was formally inaugurated more than two months ago by Greece's public order minister, but the project has since languished. Human rights groups have heavily criticized Greece over the fence, and for plans to intern illegal immigrants in former military bases pending deportation. The debt-crippled country is the European Union's main entry point for illegal immigrants, mostly from Asia and Africa

Greece-Turkey border: A pocket-sized section of a 12 kilometer-long planed fence that Greece is planning to build along its northeastern border with Turkey to keep out illegal immigrants is seen outside the village of Kastanies at the Greek-Turkish border on April 11, 2012. The 2 meter-long stretch was formally inaugurated more than two months ago by Greece's public order minister, but the project has since languished. Human rights groups have heavily criticized Greece over the fence, and for plans to intern illegal immigrants in former military bases pending deportation. The debt-crippled country is the European Union's main entry point for illegal immigrants, mostly from Asia and Africa

Hong Kong-China border: This picture taken in Hong Kong on February 13, 2017 shows the border fence with Shenzhen, China (background)

Hong Kong-China border: This picture taken in Hong Kong on February 13, 2017 shows the border fence with Shenzhen, China (background)

Hungary-Croatia border: Local police officials petrol in front of a part of the border fence on the Hungarian-Croatian border near Illocska village on February 23, 2017. The Hungarian defence forces have been performing construction and security tasks along the whole length of the more than 300-km-long temporary security barrier since July 2015. Several thousand soldiers patrol the border sections 24 hours a day, participating in search and sweep operations and securing the surveillance of the area of responsibility with UAVs and rotary-wing aircraft

Hungary-Croatia border: Local police officials petrol in front of a part of the border fence on the Hungarian-Croatian border near Illocska village on February 23, 2017. The Hungarian defence forces have been performing construction and security tasks along the whole length of the more than 300-km-long temporary security barrier since July 2015. Several thousand soldiers patrol the border sections 24 hours a day, participating in search and sweep operations and securing the surveillance of the area of responsibility with UAVs and rotary-wing aircraft

India-Myanmar border: This photograph taken on February 19, 2014, shows a sign on the border between Myanmar and India at Pangsau Pass, Saigang State, Northern Myanmar

India-Myanmar border: This photograph taken on February 19, 2014, shows a sign on the border between Myanmar and India at Pangsau Pass, Saigang State, Northern Myanmar

India-Bangladesh border: In this photograph taken on February 9, 2017, Indian Border Security Force (BSF) personnel take part in a routine patrol near the India-Bangladesh border in the village of Lankamura, on the outskirts of Agartala

India-Bangladesh border: In this photograph taken on February 9, 2017, Indian Border Security Force (BSF) personnel take part in a routine patrol near the India-Bangladesh border in the village of Lankamura, on the outskirts of Agartala

A picture taken on March 9, 2014 shows a general view of the fencing along the southern Israeli border with Egypt near the Red Sea resort of Eilat

A picture taken on March 9, 2014 shows a general view of the fencing along the southern Israeli border with Egypt near the Red Sea resort of Eilat

Israel-West Bank border: A picture taken near the southern kibbutz of Lahav on February 7, 2017, shows workers building a new section of the controversial Israeli separation wall dividing Israel from the West Bank

Israel-West Bank border: A picture taken near the southern kibbutz of Lahav on February 7, 2017, shows workers building a new section of the controversial Israeli separation wall dividing Israel from the West Bank

A gas station near the US/Canada border March 2, 2017, in the border town of Pohenegamook, Quebec. Local residents from Pohenegamook must cross through US customs to buy gas. A boundary stone can be seen just to the left of the sign showing the price of gas

A gas station near the US/Canada border March 2, 2017, in the border town of Pohenegamook, Quebec. Local residents from Pohenegamook must cross through US customs to buy gas. A boundary stone can be seen just to the left of the sign showing the price of gas

US-Mexico border: This combination of pictures shows the eight prototypes of US President Donald Trump's US-Mexico border wall being built near San Diego, in the US, seen from across the border from Tijuana, Mexico, on October 22, 2017. Following up on President Donald Trump's campaign promise to build a wall along the entire 3,200 kilometre (2,000 mile) Mexican frontier, the Department of Homeland Security began building prototypes for the barrier along the border in San Diego and Imperial counties, as it announced in August

US-Mexico border: This combination of pictures shows the eight prototypes of US President Donald Trump's US-Mexico border wall being built near San Diego, in the US, seen from across the border from Tijuana, Mexico, on October 22, 2017. Following up on President Donald Trump's campaign promise to build a wall along the entire 3,200 kilometre (2,000 mile) Mexican frontier, the Department of Homeland Security began building prototypes for the barrier along the border in San Diego and Imperial counties, as it announced in August