The US border with Mexico stretches 2,000 miles from the Pacific Ocean to the Gulf of Mexico. It crosses four states and some of the most inhospitable terrain imaginable. Hundreds of millions of people cross it each year, making it the busiest border in the world. Yet it remains something of an enigma, and a flashpoint in the current political climate. Relatively few people ever see it, yet almost everyone has an opinion on it.

This captivates Edoardo Delille and Giulia Piermartiri, who spent a fair amount of time in the American southwest during the 2016 presidential campaign. The two Italian photographers found themselves drawn to the border and it's almost mythical status, but wanted to look beyond the rhetoric and stereotypes to the lives shaped by it. They spent nine days with paramilitary militia members patrolling the border, migrants crossing it, and volunteers ensuring they make it across alive. The intimate photos in their series Far South humanize a topic too often reduced to talking points.

“Far South speaks to the two faces of a divided country,” Piermartiri says. “On one side they’re trying to protect their country. On the other, they’re trying to protect life.”

Some 350 million or so people cross the border legally each year. No one knows just how many do so illegally. The US Border Patrol apprehended 408,000 people (one-quarter of them children) last year and discovered at least 333 corpses and skeletons. That's down from 1.6 million apprehensions in 2000, and the figure has continued dwindling since President Trump took office. Yet building a "big, beautiful wall" remains a top priority for him.

It was Trump who brought Delille and Piermartiri to the southwest from Florence, Italy, last summer. The Guardian dispatched them to photograph Mexican-American Trump supporters for a news story. Before leaving Italy, they researched other subjects they might photograph, and grew fascinated by militias like Arizona Border Recon and volunteer organizations like Water Station and Samaritans.

Army veteran Tim Foley marshaled the Arizona Border Recon six years ago because he felt the US government wasn't doing enough to secure the border. The former cops and soldiers patrol the desert, looking for smugglers and migrants. Members of Water Station maintain a network of roughly 100 drums of water for migrants, while Samaritans roam the area with food, water, diapers, and other supplies for those making the crossing. Whatever their views, all of these people are trying to protect something, Piermartiri says. "What’s different," he says, "is what they’re choosing to protect.”

The two photographers spent a week in the desert outside Sasabe, Arizona, in August with a squad of 10 armed militiamen as they patrolled the scrubland. Once, they spied figures hurrying past, but failed to catch them. The men passed time sharing stories of past exploits. Although hospitable, the photographers got the sense they were not to be messed with. “They want to make America great again,” Piermartiri says.

The two days they spent with the volunteers near Nogales, Arizona, couldn't have been more different. They joined Samaritans following a trail of cast-off socks, rucksacks and shoes. They didn't find anyone, but left water and Gatorade beneath a tree just in case. The photographers also joined Water Station members roaming the Yuma Desert of California refilling water drums. The do-gooders rarely meet migrants, but occasionally find thank-you notes. This time, though, they found a couple of young men. “They were scared, tired, dehydrated," Piermartiri says. "They started crying once they understood we were not the border police.”

Delille and Piermartiri keep their opinions to themselves, and focus instead on the people who would cross the border, and those who would stop—or help—them. Both sides believe they're doing the right thing, and their views divide them more than any wall.