<P> The Mexico--United States barrier is a series of walls and fences along the Mexico--United States border aimed at preventing illegal crossings from Mexico into the United States . The barrier is not one contiguous structure, but a grouping of relatively short physical walls, secured in between with a "virtual fence" which includes a system of sensors and cameras monitored by the United States Border Patrol . As of January 2009, U.S. Customs and Border Protection reported that it had more than 580 miles (930 km) of barriers in place . The total length of the continental border is 1,989 miles (3,201 km). </P> <P> The barriers were built from 1994 as part of three larger "Operations" to taper transportation of illegal drugs manufactured in Latin America and immigration: Operation Gatekeeper in California, Operation Hold - the - Line in Texas, and Operation Safeguard in Arizona . </P>

How much of the us southern border is fenced