They started not long after the shelter-in-place order was lifted. One by one, the students carried heavy stones and laid them to rest on the grass. There was a stone for Jamie and a stone for Lauren. One for Reema and one for Jeremy and another for Maxine. Altogether they brought 32 stones, each to mark the memory of a person who’d been killed just hours earlier, in a mass shooting at Virginia Polytechnic Institute and State University in Blacksburg, Virginia.

The students lugging the stones belonged to Hokies United, a campus group that raised money and volunteered in times of emergency. They’d responded when planes hit New York in 2001; and three years later when a tsunami swallowed parts of coastal South Asia; and again the following year, when a hurricane ravaged New Orleans. The campus newspaper would one day write that the group embodied the Virginia Tech motto, “Ut Prosim” — “That I May Serve.”

Now, in the wake of their own crisis, Hokies United mobilized. The story goes that a few students with the group went to Tom Tillar, who was then the vice president of the alumni association. Their idea was to gather the blocks of limestone they would need for their plan from the nearby Blacksburg quarry.

“You don’t have time,” Tillar told them. New buildings were going up at Virginia Tech; they could mine one of the sites. “I’ll cover you if you get in trouble,” Tillar said.

With evening approaching, the students found their rocks at a construction site on campus. They set down to hauling them back to the Drillfield, the main quad and heart of the campus, where they arranged them in an arc. The work was exhausting. The rocks that the Hokies United crew carried weighed as much as 70 pounds.

Nearly a month after the shooting, the semicircle of stones remained. The grass around them grew so tall that the groundskeepers had to move the mementos, trim the grass, and then place the items back again. Chip Somodevilla/Getty Images

Anyone at Virginia Tech could tell you that these were not just any mini-boulders. Norris Hall and many of the other buildings on Virginia Tech’s campus are clad in blocks of “Hokie Stone” — mottled gray limestone that comes from a quarry a few miles down the road in Blacksburg. Limestone is composed mainly of the remains of primordial marine creatures that once roamed the ocean floor. “The fossils of ancient gastropods, clams and possibly trilobites can be found within the walls of the buildings,” a student journalist once wrote after interviewing a geology professor about Hokie Stone. Today, it’s ingrained in Virginia Tech’s culture, sold in wedges at the bookstore, touched by football players as a good luck charm before games.

“Hokie Stone is Virginia Tech,” another geology professor has said, “and Virginia Tech is Hokie Stone.”

The Hokie Stones that the students laid out in a crescent that first night had a magnetic pull. In the following days, people brought flowers and paper cranes, birthday cards and blown-out eggs, volleyballs and woven baskets and American flags on sticks. They placed the tokens on the stones, offerings at an altar.

Uma Loganathan came to see the stones. Her father was the engineering professor G. V. Loganathan, who’d been killed alongside nine of his students while he taught a class.

“There was something very raw, very primal, about what they did,” she said, adding “I remember thinking at the time that it looked kind of like a graveyard, but maybe that was the point.”

After the first 32 stones were placed, a student put down one more. The sociology major who is said to have added the 33rd rock intended it to remember the shooter, who was also a student. Someone who did not agree with this gesture took the stone away. The student who had put it there wrote to the school newspaper, vowing to replace the stone as many times as necessary. In the end, the dispute settled itself as informally as the memorial had been commissioned. The 33rd stone “at some point, disappeared, was returned a second time, disappeared again, and never came back,” recalls Mark Owczarski, an official with the college.

Mourners were divided over the 33rd stone placed for the shooter. The student who put it there felt he was a part of the Virginia Tech community, too. University administrators say the school officially remembers 32 lives taken that day. Scott Olson/Getty Images

There is no handbook for memorializing the unthinkable. After the 1999 mass shooting at Columbine High School in Littleton, Colorado, a carpenter staked 15 crosses into the top of a hill; the two representing the shooters were later torn down. In 2012, toys and letters from around the world poured into Newtown, Connecticut, a flood of good intentions that soon overwhelmed townspeople as they sorted through their grief.

Without realizing it, the kids at Virginia Tech were propelled by the same instinct that leaves mourners in America’s cities searching their surroundings for a way to honor shooting victims whose deaths often go unnoticed outside their neighborhoods. In Lexington, Kentucky, last fall, high schoolers laced track shoes to a chain link fence in homage to a slain 15-year-old runner, Trinity Gay. After a homicide in New York City, lampposts sprouted roses and sidewalks glittered with liquor bottles. In Cincinnati, a menagerie of stuffed animals was deployed to guard the home of a 9-year-old.

Most makeshift memorials fade with weather and time. Providence blessed Hokies United with more durable material. For months, the stones remained where the students had placed them on the Drillfield, soon halfway buried under mementos. So many people came to kneel and to pray and to cry that their footsteps carved pathways of dirt into the green grass.

The stones sit buried under tribute items on the Drillfield in front of Burruss Hall. Chip Somodevilla/Getty Images

Originally, the university planned to erect an official memorial elsewhere on campus. Perhaps a wall. Or maybe a sculpture. Matthew Gart, the campus landscape architect at the time, was one of the members of the committee tasked with coming up with a proper tribute to the victims. He remembers the president of the student government coming to the committee with a plea. “They really had an emotional attachment to the temporary memorial, with the 32 stones in the arc.” The committee decided its job was to make the formation permanent.

All summer, Gart and his grounds crew worked on the memorial site. Surveyors mapped out the lawn. A contractor volunteered his labor. Workers added gravel and paved pathways, installed lights and planted shrubs. At the quarry, masons split and cut 32 new stones, sized for eternity, each weighing 300 pounds. The stones were polished and engraved with the victims’ names. Then they were placed in exactly the same configuration as the students had originally laid the smaller rocks on that first night.

The permanent memorial was dedicated with a ceremony on August 19, 2007, four months and three days after the massacre. Thousands of people gathered on the lawn that day, sporting their Hokie colors of maroon and orange. The university president spoke. A bell tolled 32 times. Each original stone had been placed in a mahogany box with a hinged lid, like a miniature coffin. Later, the boxes would be delivered to the families of the victims.

Uma Loganathan can hardly remember the dedication; grief seems to have blurred many of her memories from that time. What she does remember is that first semicircle of stones set earnestly upon the grass, their rough edges befitting of her sorrow.

“When the structure was first set up,” she said, “it didn’t have all of these neat pathways and these plants. It wasn’t this carefully groomed, meticulous space. It was very rough. I think I like the original better.”