Donald Trump this week repeated his pledge to build a 2,000-mile-long border wall, telling Stephen Colbert that it would be a "big and beautiful" project and that he's going to get Mexico to pay for it. (check's in the mail, gringo).

Trump says the wall is the best way to keep out criminals, unauthorized immigrants and rapists. But since the fall of the Berlin Wall, has anyone considered what it means to close a border in the modern age?

South America might offer a real world preview of what Trump's blabbering about.

In Venezuela, President Nicolas Maduro started¬†to unilaterally shut down the¬†border with Colombia on Aug. 20, arguing √† la¬†Trump, that the border had to be closed to stop¬†criminals ‚ÄĒ specifically paramilitaries and smugglers‚ÄĒfrom entering the country.¬†Venezuela lacks the resources to build an actual wall (and unlike Trump, couldn't convince Mexico to pay for it),¬†so Maduro's government has made do by¬†placing metal barricades along¬†roads and bridges connecting the two countries.

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Along the largest border crossing near the city of Cucuta, vehicle traffick has been restricted to ambulances and a handful school buses. People who want to travel to Venezuela on foot must wait for several hours to be allowed in, and immigration officials are severely restricting the number of visitors allowed to enter.

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A month into the border shut down, hundreds of small businesses on the Colombian side of the border have shuttered. They relied on Venezuelan shoppers and cheap Venezuelan products. The border closure starved them of both.

Money exchangers in Cucuta have also been pinched. With only a trickle of people crossing the border, demand for their services has dropped sharply.

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Gasoline, which was imported from Venezuela ‚ÄĒmost of it illegally‚ÄĒis now scarce in the border town of Cucuta. That's led to long lines at the city's gas stations.

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Colombian mines that exported coal to Europe through Venezuela are now stuck with an estimated 220,000 tones of coal that's piling up, unable to get to market.

The situation isn't much better in Venezuela, where businesses that used to sell leather goods and clothes to Colombians are also shutting down, or staying open, but getting hardly any clients.

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But some people are finding ways to get around the border controls, which have been described by Colombian officials as "South America's Berlin Wall."

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This family of six took a dusty trail that leads out of Venezuela, and crossed a river into Colombia. They said that they had to bribe Venezuelan National Guardsmen to cross, even though they had all their documents in order. A month ago, crossing the border was easy and free.

In the town of Puerto Santander, where a river divides both countries, people wait for Venezuelan border patrols to leave the area so that they can cross the border illegally on boats.

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Some merchants are also still finding ways to smuggle their product into Colombia, where prices for most goods are much higher. Colombian police report that since the border shut down, they have confiscated 29,000 kilos of contraband beef from Venezuela. And that's just in Norte de Santander state, which covers around a fifth of the long border.

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When the border shut down started last month, Maduro expelled more than 1,400 Colombians who were living in Venezuela illegally.  He said they were deported as a measure to prevent crime.

Many are now staying in deportee camps on the Colombian side.

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So there you have it, Donald. A closed border probably doesn't work. It's bad for business and it doesn't stop illegal activity. Just the opposite, in fact. When the border is closed, everything becomes illegal.

Manuel Rueda is a correspondent for Fusion, covering Mexico and South America. He travels from donkey festivals, to salsa clubs to steamy places with cartel activity.