By Sally Hayden
LONDON, Jan 26 (Thomson Reuters Foundation) - U.S. President Donald Trump has ordered the construction of a wall along the 2,000-mile (3,200 km) long border between the United States and Mexico, saying it was necessary to stop illegal immigrants from entering the country.
Trump is not the first leader to build a wall aimed at securing his country's borders. Globally, more barriers between countries now exist than at any other time in modern history.
In 1989, after the fall of the Berlin Wall, there were only 15 border walls around the world. Today, there are 70 of them.
Notable spikes in the construction of border walls took place after the Sept. 11, 2001 attacks on the United States and the Arab Spring, academic Elisabeth Vallet told the Thomson Reuters Foundation.
Here are some more facts about border walls around the world:
* The European migrant crisis led to several border barriers being erected, including a fence on the border between Serbia and Hungary.
* Austria has built fences on its borders with both Hungary and Slovenia, which it said are necessary to manage crowds of migrants.
* In 2015, Hungary used prisoners in a high-security jail to produce razor-wire to top border fences.
* Israel's barrier with Egypt incorporates cameras and motion sensors.
* At border between India and Bangladesh there have been more than 1,000 killings over the last 15 years by the Indian border security forces.
* The type of material used to construct border walls varies, with some including razor wire, metal and sensors.
* Research carried out by the Pew Center shows that 39 percent of Americans see building a wall on the Mexican border as a very or somewhat important goal.
* Those policing borders say barriers are not necessarily effective. "Security officials say all the time, 'Show me a 10 metre wall and I'll show you an 11 metre ladder'," Reece Jones - author of "Border Walls: Security and the War on Terror in the United States, India, and Israel", told the Thomson Reuters Foundation.
(Sources: Reuters, Pew Research Center, University of Quebec academics) (Reporting by Sally Hayden @sallyhayd, Editing by Katie Nguyen. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, climate change and resilience. Visit http://news.trust.org)