When the National Gallery of Art realized that, with a major acquisition of works from the Corcoran Gallery of Art in 2014, it had one of the largest public holdings of photographer Sally Mann, efforts began on mounting her first major international exhibition. “Sally Mann: A Thousand Crossings,” which opens Sunday, covers four decades of work from the 66-year-old photographer, who initially stayed close to her childhood home in Lexington, Va., but deepened her understanding of the South by traveling more widely to ponder its fraught history in haunting photographs further enhanced by antique, experimental processes. Here, Sarah Greenough, senior curator and head of the department of photographs at the National Gallery of Art, gives insight into five of the 110 pieces included in the exhibit.

‘Deep South, Untitled (Scarred Tree),’ 1998
After chronicling her home life in west-central Virginia, Mann embarked on trips to other Southern states. While in Woodville, Miss., she captured this gauzy, early-morning shot (above) of a tree in Mississippi that had survived an attempt by someone to cut it down. “It’s like a wound from the past that remains visible, as if it were like a silent witness to another age,” Greenough says. The photo, she adds, represents one of Mann’s central themes: “The way the landscape can be a vessel for memory.”

‘On the Maury,’ 1992
The Maury River, which winds through Mann’s family farm in the Shenandoah Valley, was central to her family, whom she photographed almost exclusively in her early days. This image shows what a serene playground the river provided for her children, Greenough says. “But it also assumes an important position in her photographs, signifying themes of passage and time and death,” and this one depicts “the river propelling the family downstream, seemingly into the future and away from the camera.”

‘Battlefields, Antietam (Black Sun),’ 2001
Early this century, Mann was drawn to the Civil War battlefields in her home state. “She became fascinated with the idea: Does the earth remember?” Greenough says. “Does it bear witness in some way to the unspeakable number of people who were killed, the blood that was spilled on that landscape?” For this shot, she positioned her camera near the ground, “to give that sense of a last view a dying soldier might see.” The scratches and imperfections created by the wet-plate collodion process (a messy technique popular in the early days of photography) added their own dark metaphor (and the black sun) — “almost as if you’re looking at something shrouded in black mourning cloth.”

‘Hephaestus,’ 2008
Among the most recent works in the exhibit are enigmatic portraits of Mann’s husband, a lawyer suffering from late-onset muscular dystrophy. He was also a blacksmith, hence this portrait’s title, which is the name of the Greek god of metalworking. The quirks of the wet-plate collodion process add another layer: “The crackling and abrasion on Larry’s muscled torso convey the ravages of his disease while the silvery molten quality of the swirls in the picture seemingly allude to the idea of metalworking,” Greenough says.

‘Oak Hill Baptist 01:01,’ 2008 (printed in 2016)
Mann began to look at how race shaped Virginia by seeking out old country churches founded immediately after the Civil War, when black people could worship together for the first time without a white minister. “She discovered that many of these 19th-century churches were within a stone’s throw of her home in Lexington,” Greenough says. That includes this one, which got an otherworldly look when the image was printed on expired photo paper.

National Gallery of Art, West Building, Sixth Street and Constitution Avenue NW; Sun. through May 28, free.