the mexico-united states barrier is a series and fences along the mexico-united states border aimed at preventing illegal crossings from mexico into the united states.the barrier is not one continuous 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 580miles [93km] of barriers in place.the total length of the continental border is 1,989miles [3,201km].