Before the fence, there were obelisks – 276 monuments marking the US-Mexico border that were erected after the Mexican-American war ended in 1848.

In 2007, David Taylor, an Arizona-based artist and professor, set out to photograph them all – a task that lasted seven years and took him from the Texas, New Mexico and Chihuahua border to the Pacific Ocean, passing through cities and remote mountainous terrain.

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Taylor did this during an era of ever-growing militarisation as cartel-related violence soared and the US continued to ramp up its post-9/11 spending on border security, adding to political and cultural tensions mined by Donald Trump, who continues to demand the construction of the border wall he advocated during his successful presidential campaign.

Taylor’s photographs capture topographic diversity across 690 miles and the forbidding infrastructure overshadowing iron and stone monuments typically spaced 2.5-3.5 miles apart.

“They are a monument to conquest. We ripped off 55% of Mexico’s territory. And so our perception of them and Mexico’s perception of them was different for a long time. More and more of course, now, they’re seen as positively dignified compared to what’s going in adjacent to them.”

The frontier was surveyed over six years after the 1848 Treaty of Guadalupe Hidalgo, which saw an expansion-hungry US pay Mexico $15m to assume roughly half of its pre-war territory. The 1853 Gadsden Purchase added to the US’s holdings. The line was resurveyed in the 1890s after a series of disputes.

Taylor resists simplistic good-and-bad narratives about life on the border that fail to convey the nuances he saw while depicting the monuments. One memorable incident was an encounter near Nogales with young smugglers working as spotters. They agreed to be photographed.

“One of the two, when I finished, they had asked where the images would be published or used,” he recalled. “They said no Telemundo [a US Spanish-language television station], no periódico [newspaper] and one of the kids drew his finger across his throat – but it wasn’t a threat. It was about their expendability, that to have the picture show up in a Nogales paper the next day would mean really bad things for them. Moments like that, where you see another human being’s vulnerability and understand their circumstance in a way that’s more multidimensional than ‘oh yeah, they’re just smugglers’.”

On another occasion he met a young man and woman from Chiapas, a Mexican state that borders Guatemala. They were abandoned by their “coyote”, or smuggler, had been lost for several days and were out of food and water and desperate to reach the Arizonan cities of Tucson or Phoenix.

Facebook Twitter Pinterest Border Monument No 153 on 6 April 2012 at 12.27pm. Photograph: David Taylor

“I pointed them in the right direction, never saw them again. I wonder every day what happened to them,” Taylor said. “You meet people who have such desperate circumstances. I felt this enormous sense – still do feel this enormous sense – of luxury for my life after all the people I’ve encountered out in that space and thinking about what they go through in hopes of trying to figure out something better for themselves.”

Taylor’s Monuments images are the subject of an exhibition at The Museum of Fine Arts, Houston, until 28 January. It follows another attempt to bring a historical perspective to our understanding of the border made in 2014 when Taylor and Marcos Ramirez, a Tijuana-born artist, drove in a van along the boundary as it was in 1821, marking it with 47 obelisks of their own. Then it stretched as far north as modern-day Oregon down to Louisiana, via present-day states such as Nevada, Wyoming, Colorado and Oklahoma.

“The ways in which the discourse around the border has shifted are tied enormously to everything from our antipathy towards brown people in this country to what the caprice of our economic interests are at any given moment,” Taylor said.

“And you see it with everything from the Bracero project to bring Mexicans to the United States during World War Two to work in agricultural labour as well as other arenas, and then following that, Operation Wetback [in 1954] to remove Mexicans.”

Taylor pointed out that the US Border Patrol originated in the 1900s from attempts to enforce the 1882 Chinese Exclusion Act, which banned Chinese labourers from immigrating: “Mexicans weren’t even on the radar screen.”

One of the biggest changes in the American mentality in the past couple of decades, he said, is that the notion of border security became intertwined with anti-terrorism and stronger nativist impulses.

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“At this point what we have is a border security industrial complex, which wasn’t the case. I sort of witnessed that all happen. Border Patrol stations resembled rural law enforcement operations most of the time, you’d have 15-20 agents working out of a double-wide trailer responsible for 35 miles of border out in the desert and most of the big stations were in urban areas and that’s where enforcement occurred and people weren’t really paying attention to the outback.”

These days the entire frontier is seen as a potential threat to American safety. With Trump’s ascent, Taylor believes, US policy has “taken an alarmingly bad turn but it’s been trending in the same direction for a long while. It’s the mind of this country, it’s where we are, sadly to say”.