Jiankou, an unrestored section of the Great Wall of China, photographed near Beijing. The Great Wall is a collection of fortified barriers built over hundreds of years to protect various Chinese empires from nomadic tribes to the north. #

A girl wearing a traditional hanbok dress looks through a military fence facing toward North Korea at the Imjingak park, south of the military demarcation line and the demilitarized zone (DMZ) separating North and South Korea, on February 19, 2015. Many South Korean families separated during the Korean War visit the DMZ to offer prayers to their relatives in North Korea on the occasion of the Lunar New Year. #

An aerial photo shows a section of the "Berm," or the Moroccan Western Sahara Wall, a fortified wall running 1,700 miles through parts of Morocco and the western Sahara, on January 4, 2002. The wall and an extensive minefield were built throughout the 1980s to separate Moroccan-controlled western regions from areas to the east controlled by the Polisario Front, a rebel group trying to push Morocco out of the western Sahara. #

A picture taken on October 18, 2016, from the eastern-Jerusalem Arab neighborhood of Issawiya shows a Palestinian youth looking on as the Palestinian Shuafat refugee camp (right) is seen behind the controversial Israeli separation wall. #

The India-Pakistan border appears as an orange line in this photograph taken by the Expedition 28 crew on the International Space Station on August 21, 2011. The fence between the two countries is floodlit for surveillance purposes. #

A then–recently constructed section of the U.S.-Mexico border fence crosses previously pristine desert sands at sunrise on March 14, 2009, between Yuma, Arizona, and Calexico, California. The section of barrier stands 15 feet tall and sits on top of the sand so it can be lifted by a machine and repositioned whenever the migrating desert dunes begin to bury it. #

The Spanish Guardia Civil watch as would-be immigrants from Africa sit atop a fence after scrambling over two other border barriers on Spain's tiny North African territory of Melilla on August 13, 2014. About 600 people tried to scale the triple-layer, six-meter-high razor-wire barrier that separates Morocco from Melilla in a predawn assault, said Irene Flores, the spokeswoman for the Spanish government in Melilla. More than 60 of them had perched on the top of the border fence, she told Agence France-Presse. #

The remains of Hadrian's Wall snake across the rugged landscape beneath a dark overcast sky in Northumberland, England, on August 6, 2018. Hadrian's Wall was a Roman defense fortification built in the first century A.D., spanning the entire width of England from the Irish Sea to the North Sea. It was designed as a defense against people from the north. #

People chat over coffee next to a fortified section of the buffer zone on the southern, Greek side of the divided city of Nicosia, Cyprus, on March 7, 2017. Nicosia has been divided into a Greek, southern side and Turkish, northern side ever since the brief but devastating war of 1974. Since then, United Nations peacekeepers have maintained a buffer zone that runs through the city and across the entire island to keep the factions apart. In the south, the Greek-dominated Republic of Cyprus is recognized internationally and is a member of the European Union, while in the north, the self-proclaimed Turkish Republic of Northern Cyprus is recognized only by Turkey, which also has tens of thousands of troops stationed there. #

A silver Jeep Cherokee that suspected smugglers were attempting to drive over a 14-foot-high section of the U.S.-Mexico border fence sits stuck at the top of a makeshift ramp on October 31, 2012, near Yuma, Arizona. U.S. Border Patrol agents from the Yuma station seized both the ramp and the vehicle, which stalled at the top of the ramp after it became high centered. The two suspects fled into Mexico when the agents arrived at the scene. #

Indian Border Security Force soldiers stand guard along fencing near the India-Pakistan Chachwal border outpost some 65 kilometers north of Jammu, India, on August 2, 2012. The border dividing the two countries, which have fought three wars since 1947, is one of the most militarized areas in the world. #

A migrant runs after entering Hungary by crossing the temporary protection fence along the Hungarian-Serbian border as a Hungarian police car approaches in Röszke, Hungary, on September 7, 2015. #

A man attacks the Berlin Wall with a pickax on the night of November 9, 1989, as news spread rapidly that the East German government was to start granting exit visas to anyone who wanted to go to West Germany. The announcement was misinterpreted as meaning the border was now open, and East German border guards were unable to stop the rush of people to the wall. Within hours, people were smashing sections of the wall with their own hand tools, and these first cracks in the wall led to the complete opening of the border within days. #

Residents of Naco, Arizona, join residents of Naco, Sonora, Mexico, for a volleyball match during the fourth "Fiesta Binacional" at the fence that separates the United States (left) and Mexico (right) on April 14, 2007. The net is set up on top of the border fence. #

The "peace walls" that divide Catholic and Protestant communities, photographed in Belfast, Northern Ireland, on February 22, 2017. Originally built in 1969, most of the so-called peace walls are still intact and indeed necessary to provide shelter from attack from opposing sides even after the Good Friday Agreement was signed in 1998. #

A Ukrainian border-guard officer speaks on a phone near a national flag attached to the fence on the Ukrainian-Russian border near Hoptivka, Kharkiv region, eastern Ukraine, on April 18, 2015. The flimsy, razor-wire-topped fences that popped up along bare expanses of Ukraine’s eastern frontier were the first line of defense against a much-feared Russian invasion. #

A Zimbabwean immigrant climbs through a barbed-wire fence while illegally crossing into South Africa near Musina on May 27, 2008. Facing economic strife and political oppression at home, Zimbabweans flooded across the border, despite violent attacks against foreign immigrants in South Africa. #

A young Palestinian shepherd leads his flock in front of Israel's barrier near the Shufat refugee camp and the settlement of Pisgat Zeev (background) in East Jerusalem on January 15, 2016. #

A Palestinian boy perches on a concrete outcrop as he watches the wall separating the southern Gaza Strip town of Rafah and Egypt blow up near a crowd of people wanting to cross the border into Egypt on September 14, 2005. Hamas militants blew a gaping hole in the concrete barrier, which had been hastily erected in a bid to stop Palestinians from surging across the Gaza Strip into Egypt, witnesses said. A series of giant concrete blocks had been placed at the Rafah border overnight as Egyptian and Palestinian officials attempted to put a lid on the scenes of chaos. #

A visitor films through a fence decorated with ribbons carrying messages that visitors left wishing for the reunification of the two Koreas at the Imjingak pavilion near the border with North Korea in Paju, South Korea, on April 15, 2016. #

Two women hug each other through the wall during the "Not Walls" demonstration by activists in the United States in front of the wall that divides Ciudad Juarez, Mexico, from Sunland Park, New Mexico, on October 23, 2017. #