according to images released by the U.S. Customs and Border Protection in 2011. The types of fencing includes wire mesh, chain link, post and rail, sheet piling, concrete barriers for vehicles and X-shaped steel beams for livestock.

Trump has said he wants a concrete barrier as high as 55 feet tall and has described his proposed wall as "impenetrable, physical, tall, powerful, beautiful."

Under the Secure Fence Act, the pedestrian border fencing completed in fiscal year 2007 was estimated to cost about $2.8 million per mile, according to a 2009 report from the Government Accountability Office. It was constructed using mostly the U.S. Army Corps of Engineers and the National Guard, according to the Congressional Research Service. The 2009 report also found that fencing constructed in fiscal year 2008, whichmostly used private contractors, cost about $3.9 million per mile.

“Beginning today, the United States of America gets back control of its borders, gets back its borders,” Trump said Wednesday at the Department of Homeland Security after signing two executive orders related to immigration. The executive order calls for the immediate construction of a physical wall on the southern border to achieve "operational control," which it defines as "the prevention of all unlawful entries into the United States, including entries by terrorists, other unlawful aliens, instruments of terrorism, narcotics, and other contraband.”

Building a new 1,000-mile wall could cost as much as $40 billion, according to an analysis published in the MIT Technology Review. Maintenance of barriers along the southern border will also be costly. The Congressional Research Service estimated