The US and Mexico share a 3,200km (2,000 mile) border, of which about a third is separated by fencing.
The US government is to increase security at the border with Mexico in an attempt to combat drug cartels.
US immigration, customs, anti-drug agents and gun law enforcement officers will be reinforced as part of a $700m undertaking.
The US Horse Patrol provides support to other border patrol agents, covering the most remote areas that are inaccessible to vehicles.
The force was set up in 1920s. Today their main focus is on stopping drugs getting into the US and tracking illegal immigrants.
Gang violence is surging in Mexico where some 40,000 soldiers have been deployed to root out drug cartels. Thousands are in Ciudad Juarez.
Efforts are under way to rebuild the entire structure of the Mexican police force, but the process is expected to take years.
Ciudad Juarez is the most violent city in Mexico. About 2,000 people were killed here in the past 14 months in drug-related violence.
More than 6,000 people died in violence related to organised crime last year in Mexico. Some are buried in unmarked graves.