A man with a little salt in his black beard stood at the base of Minneapolis artist Siah Armajani's freshly repainted Irene Hixon Whitney Bridge last weekend. Pointing a smartphone toward a woman standing atop the bridge's stairwell, he shouted, sweetly: "Mira que linda!" ("Look how pretty she is!")

The woman smiled, posing with delight. The man clicked a few photos before slipping the phone back in his pocket. He ascended the stairs to embrace the woman. Then the bridge led them over Interstate 94, from Loring Park to the Minneapolis Sculpture Garden.

Unveiled in 1988, the Hixon bridge was influenced by German philosopher Martin Heidegger, Armajani explained in an interview last week. Heidegger had a theory that illuminates the thinking behind the bridge, with eight lanes of highway running below. The traffic is as relevant to the experience as the sky above and the couple stopping to snap photos before traveling along. "Heidegger says that 'a bridge is an entity which brings whatever it is before the bridge to what is after the bridge, in addition to what it brings from above the bridge, and what is below the bridge,' " Armajani said.

The iconic Minneapolis bridge was touched up recently in preparation for the Walker Art Center's gigantic "Siah Armajani: Follow this Line" retrospective, opening Sunday. With 35 works spanning six decades, the Walker has the world's largest institutional collection of Armajani's work. The loosely arranged exhibition features more than 100 works including some of the artist's earliest pieces, created when he was a young activist living in Tehran. It surveys the architectural focus of Armajani's work in the 1970s, '80s and '90s to his overtly political sculptures of the 2000s onward. The show will travel to New York's Met Breuer museum in February.

Armajani is notoriously private, very much opposed to being photographed, insisting that the art represent his story. No wonder it took some persuading to bring this show together, with the Walker making three attempts over many years.

The third and winning try was cemented by the Walker's former executive director, who visited Armajani's Minneapolis studio shortly after arriving in Minneapolis in 2007.

"Olga Viso came over to my studio and she said, 'You have something against Walker?' " Armajani recalled.

"And I said, 'No I don't.' And she said, 'Well, why won't you have a retrospective here?' And I agreed."

Building from politics

Born in Tehran in 1939, Armajani worked primarily in painting before 1960. He was influenced by traditional Persian bookbinding, suffusing his art with ordinary Persian script rather than highbrow calligraphy.

Politics were another recurring theme, with Armajani fiercely opposing the Shah's reinstatement in 1953 when democratically elected Prime Minister Mohammad Mosaddegh was overthrown in a coup. The 1957 piece "Night Letter #1" leaves little doubt to the artist's thinking: "Mossadegh's way / Oil is ours / Independence is ours / Freedom is ours."

Then Armajani's family began to worry for his safety. Armed guards escorted him to a plane in 1960, exiling Armajani from his homeland.

He moved to Minnesota and enrolled at Macalester College, where his uncle worked in the history department. As a philosophy major, Armajani learned about American pragmatist John Dewey and avant-garde composer John Cage. He soaked up the French existentialists' writing on solitude, something Armajani said he experienced himself living in Minnesota. And he studied the Abstract Expressionists, who guided some of his 1960s paintings.

Armajani's relationship with the Walker goes all the way back to its 1962 purchase of "Prayer," an abstract painting featuring a mix of Persian and American influences. The work became a part of the Walker's painting biennial under then-director Martin Friedman, who wrote Armajani an ill-fated check for $500. Armajani was working on another piece in his studio, he recalled, when he inadvertently cleaned his pen on the financial document. "It was the check! I didn't notice it! I went to bank and they said, 'We cannot accept this — you covered the signature.' "

So the artist went back to Friedman and requested a new check. Armajani has enjoyed a close relationship with the Walker ever since.

As the 1960s waned, Armajani started experimenting with architectural structures, creating small-scale models of bridges and gazebos. He built his first full-scale bridge in 1968 on his mother-in-law's property in White Bear Lake. Made of stained balsa wood, the bridge begins with a wide rectangular opening, eventually becoming tighter and tighter until there's hardly any room to escape.

A permanent structure in Loring Park, "Gazebo for Four Anarchists: Mary Nardini, Irma Sanchini, William James Sidis, Carlo Valdinoci" (1991) is an open structure with bars reminiscent of a prison cell, a metaphor for locking away political prisoners. As Armajani sees it, "All of my work since Day One has been political."

'Elusive, ambiguous' works

Back in the '90s, Armajani often described his practice as open, available and useful. "I had minimized that hardness — my own ego — to bring about a useful object," he said.

Then something started to shift. "I became closed, my work became closed, elusive, ambiguous," he said.

His 2004-05 piece "Fallujah" captures the artist's virulent opposition to the Iraq war (the piece also references Picasso's 1937 "Guernica"). A rectangular glass cube holds a silent rocking horse within, the entire structure propped askew by two toppled wooden chairs. To one side there's a staircase with glass planks, leading to nowhere. There are pillows, but no one is able to rest their heads. At 16 feet tall, the sculpture barely fits into the Walker gallery.

More recent works retain that political edge. In the series "Seven Rooms of Hospitality" (2016-present), Armajani references French philosopher Jacques Derrida's theory on hospitality, which suggests a measure of hostility from the host.

One piece, "Room for Asylum Seekers," recreates a refrigerated truck used in 2015 by smugglers in Europe who picked up 71 refugees from Afghanistan, Iraq, Iran and Syria, locked them inside, then abandoned them to die of suffocation. The side of the truck reads: "71 Asylum Seekers — 60 men — 8 women — 3 children — All Dead." The work is eerie and very different from Armajani's functional bridges.

The Walker's retrospective was organized by assistant curator Victoria Sung and the Met Breuer's Clare Davies. Sung and Davies settled on the exhibition title — "Follow This Line" — after Armajani told them about a game he played during his childhood in Tehran. He and friends would run through the city, drawing lines with pencils along the city's walls. Then they would follow the lines again for fun.

"We really liked the phrase as an invitation to visitors," Sung said, "to follow the line of the artist across time, geographies and space."

The title also hits the "idea of exile," Sung said, capturing the body's relationship to displacement and space. "Having moved from Iran to Minneapolis, Siah is existing in this space in between the two," she said.

Sung first arrived at Armajani's studio three years ago, during her first week on the job at the Walker. "Victoria and Clare, they are in their 30s, and I am almost 80," Armajani remarked, with wonder in his eyes. "They're 50 years my junior. It's amazing!"

Correction: A previous version mischaracterized a crime that inspired the artwork by Siah Armajani.