Soldiers participating in "Operation Faithful Patriot" are working with US Customs and Border Patrol officers to install the fending, according to the Department of Defense.
During a Saturday campaign rally in Montana, President Trump said "Mexico is trying, they are trying but we're different, we have our military on the border," adding "And I noticed all that beautiful barbed wire going up today. Barbed wire, used properly, can be a beautiful sight."
A spokesman for the US Border Patrol told the New York Post that the fencing was part of "necessary preparations" for the caravans.
Around 900 troops have arrived at the US-Mexico border since the Trump administration announced the deployment on October 26.
The president vowed the forces would block the caravans, which contain thousands of migrants, from entering US turf.
Military units are heading to outposts along the border from Texas to California.
After saying about 5,000 active-duty troops would be deployed as part of Operation Faithful Patriot, Trump on Wednesday boosted the number from 10,000 to 15,000.
A separate contingent of about 2,100 National Guard troops had already been deployed to work with Border Patrol in anticipation of the caravans, which have about 7,000 people total, according to the Defense Department. -NY Post