"We will soon begin the construction of a great wall along our southern border," President Donald Trump said in his address to Congress on Feb. 28, following up on his hallmark campaign promise. But in parts of California, Arizona, and Texas, a wall already exists.

The pedestrian border in Nogales, Arizona. | Nov. 7, 2016 | (REUTERS/Mike Blake)

The barriers along the U.S.-Mexico border, some of which date back to 1994, are discontinuous. But put together, they would cover about 580 miles of the nearly 2,000-mile border that stretches from San Diego, California, to Brownsville, Texas.

The structures vary as much as the landscapes on which they are built. They can be imposing — cement, steel mesh, corrugated metal — or more of a suggestion — a low fence, signs, security cameras. In some places the wall literally severs towns in half; in other places the divide is more personal, splitting communities, business, and families that once lived and worked together.

A woman In Tijuana talks to her relatives across a fence. | Nov. 13, 2016 | (REUTERS/Jorge Duenes)

Trump's proposed wall — a series of fences and walls — is projected to cost as much as $21.6 billion and take more than three years to build, according to a U.S. Department of Homeland Security report. And it isn't yet clear who will pay for it. But U.S. residents along the border are ideologically divided. "It's just a waste of money," Basilisa Valdez, a Mexican-born Texas resident, told the Texas Tribune. "That's not going to stop the people from coming over. There's always a way to come in."

A resident in Brownsville, Texas, points out that the wall they already have isn't doing its job securing the border. "What makes them think a new one will [work]?," asked farmer Bonnie Elbert.

An Arizona cattle rancher disagrees. "We need a wall," Jim Chilton told The Associated Press, adding that it should be part of a larger plan. "We need Border Patrol to be down there all the time. We just need to secure that international boundary at the border, period."

As Trump works to fulfill his promise, here's a look at the border walls that already exist along our southern border.

A gap in the U.S.-Mexico border fence outside Jacumba, California. | Nov. 7, 2016 | (REUTERS/Mike Blake)

A road abruptly ends next to a sign for a cattle ranch near Douglas, Arizona. | Oct. 10, 2016 | (REUTERS/Mike Blake SEARCH )

A newly-built section of the border fence in Ciudad Juarez, Mexico. | Jan. 25, 2017 ( REUTERS/Jose Luis Gonzalez)

The backyard of a home in Brownsville, Texas, faces the border fence. | Aug. 5, 2014 | (REUTERS/Shannon Stapleton)

The border near Calexico, California. | Feb. 9, 2017 | (REUTERS/Mike Blake)

The border fence in Mexicali, Mexico, painted sky blue. | April 9, 2016 | (REUTERS/Sandy Huffaker)

The border in Calexico, California. | Oct. 8, 2016 | (REUTERS/Mike Blake)

A San Diego beach. | Nov. 13, 2016 | (REUTERS/Jorge Duenes)

A fence separates the border towns Nogales, Arizona (left), and Nogales, Mexico (right). | Oct. 9, 2016 | (REUTERS/Mike Blake)