Sarah Elizabeth Adams was around 5 when her mother was sold to a slave dealer in Lynchburg, Va. The auction took place in the mid-1840s, in the town of Marion, Va. Sallie, as she was called, was herself sold that day, but not with her mother: A man named Thomas Thurman purchased Sallie to take care of his sick wife. She would never see her mother again. For the remainder of her childhood, whenever she could, Sallie would slip away and find solace under a tall white-oak tree. All alone, she would wrap her arms around the tree’s wide trunk and cry. The tree became the place where she would recall the names and faces of her family members sold away; a place where she could grieve, but also a place where she could find shade and respite from her sorrow.

This story was told many years later by Sallie’s granddaughter, Evelyn Thompson Lawrence, a local educator and historian in Marion. Thompson’s efforts led to the founding of the Mount Pleasant Heritage Museum — housed in a former black Methodist church that Sallie and other freed men and women founded after the Civil War — to preserve the history and culture of African-Americans in the county. We know that Sallie was sold at an auction held at the Smyth County Courthouse, a brick building that was torn down after the turn of the century, when Mari­on’s current courthouse was constructed. And yet many details of her story have been lost: We don’t know exactly what happened to Sallie’s mother, or how much Sallie was sold for, or even exactly when the auction took place.

Sallie and her family were among the 1.2 million enslaved men, women and children sold in the United States between approximately 1760 and 1860, according to the historian Michael Tadman. After the American Revolution, cotton production grew rapidly, and demand for enslaved workers on the vast plantations of the Deep South intensified. This, along with the ban on importation of enslaved Africans that took effect in 1808, largely led to the rapid growth of the domestic slave trade. Auctions and the sales of enslaved people could be found near or along the major ports where enslaved Africans landed, including Richmond, Va.; New Orleans; Savannah, Ga.; and Charleston, S.C. But the enslaved were also sold in Massachusetts, Rhode Island, New Jersey and at New York City’s 18th-century open-air Meal Market on Wall Street. The sales took place all over the growing nation — in taverns, town squares and train stations, on riverbanks and by the side of the road. Before being sold, the enslaved were often kept in pens or private jails, sometimes for days or weeks. Then they were sold directly from the pens or marched to a nearby auction. Thousands of sales took place each year, right in the hearts of American cities and towns, on the steps of courthouses and city halls. As the historian Steven Deyle puts it, slave auctions were “a regu­lar part of everyday life.”

Many American fortunes were made this way. The largest slave-trading firm during the late 1820s and 1830s was Franklin & Armfield, whose Virginia offices and infamous holding pen were located at 1315 Duke Street in Alexandria. In their heyday, Isaac Franklin and John Armfield sold between 1,000 and 2,000 enslaved people per year, and by the time Franklin died in 1846, his estate was valued at $710,000 — almost $24 million today — a fortune largely earned through the slave trade.

A photograph, circa 1865, of the slave-trading firm Price, Birch & Company in Alexandria, Va. Franklin & Armfield, one of the largest slave trading firms in the country, was headquartered in the same building until it was sold to a partner of Price, Birch & Company.

Slave trading was a lucrative business, yet for the enslaved people themselves, the auction block represented a particular horror — the end to life as they knew it. Family was one of the few bright spots in the long night of slavery, and the auction was the event that ripped enslaved families apart. The very prospect of it cast a specter over the enslaved population like a slowly dilapidating roof: At any time, it could come down and destroy the inhabitants of an already-fragile dwelling. Sales were so common that some enslaved people could be sold as many as six times in their lives, if not more, often with little warning and no chance to say goodbye. In some cases, infants were literally torn from wailing mothers.

We know from enslaved people themselves — the relative few who were able to write or otherwise tell their stories — that the auction block was even more feared than a lashing. “Common as are slave-auctions in the Southern states,” wrote one formerly enslaved man, Josiah Henson, “the full misery of the event — of the scenes which precede and succeed it — is never understood till the actual experience comes.” The New Deal-era Slave Narratives project, funded by the Works Progress Administration, is full of terrifying memories like this one, from a formerly enslaved woman in Arkansas named Will Ann Rogers: “When Ma was a young woman, she said they put her on a block and sold her. They auctioned her off at Richmond, Virginia. When they sold her, her mother fainted or dropped dead, she never knowed which. She wanted to go and see her mother lying over there on the ground, and the man what bought her wouldn’t let her. He just took her on. Drove her off like cattle, I reckon.”

After the Civil War, most former auction sites quietly blended into the main streets of today. Except for the occasional marker or museum, there was no record of the horror of separation suffered by many black families. The emphasis on national unity and reconstruction created a desire to paper over the atrocities of the past, and many of these sites were forgotten. They were not forgotten, though, by the formerly enslaved people who had been sold there, or by their families. Immediately upon Emancipation in 1863 and the end of the war in 1865, many of these newly freed men and women set out on foot searching earnestly for their loved ones, and often the place they sought out first was the auction site. They took with them a lock of hair, a swath of clothing — small mementos that they had saved. They posted advertisements in newspapers and black churches searching for lost relatives. Their cry was “Help me to find my people,” as the historian Heather Andrea Williams documented in the book of the same name.

A photograph from about 1900 of the auction block on which enslaved people stood when they were sold at the St. Louis Hotel & Exchange in New Orleans.

But often the auction site was no longer there to find. The war had laid waste to much of the South; the auction blocks had largely been removed, and the auction houses that still stood had been repurposed. No one was eager to preserve these sites, or even remember them. And so they disappeared, year by year, generation by generation, until there was no living memory of what happened in these places.

Today, only a small minority of these sites have been properly docu­mented, recorded and preserved. There is no online database to find them. Countless remain completely unknown. When The New York Times Magazine asked the photographer Dannielle Bowman to document some of these sites, it quickly became clear that most of their locations could be pinpointed only through original research.

And so for the last five months, my research assistants and I at the Binghamton University/Harriet Tubman Center for the Study of Freedom and Equity have combed through archives — including volumes of narratives of the formerly enslaved, as well as post-Civil War ads placed in newspapers by the enslaved themselves — in an attempt to expand the historical record about America’s slave-auction sites. During that time, we have been able to identify fewer than 50 that have been marked and approximately 30 unmarked ones. Yet these are almost certainly just a fraction of the total, when you consider how many sales took place, over how many decades, during this chapter in American history.

Why is it important to excavate these sites? This is a question I have spent a long time considering. My second book, “The Weeping Time: Memory and the Largest Slave Auction in American History,” was about a horrifying event that took place over two days in Savannah in 1859. Four hundred thirty-six men, women and children, including 30 babies, were sold at the Savannah Ten Broeck Race Course, normally a playground for local elites. These enslaved men and women, Gullah Geechee African-Americans, had lived together for years on the plantation estates of Pierce Mease Butler, where they forged a community with its own norms, values and customs — many informed by their African heritage. But this auction, which they came to call “the weeping time,” separated them from their families and displaced them from the only “home” they had; it was a decisive moment, maybe the decisive moment, in many of their lives. Their family bonds may have mattered little to their owners, but they mattered to the enslaved. The extent to which several of them plotted and planned about how to stay together, or went looking for one another after Emancipation, spoke to the strength and resolve of black families.

An advertisement published in The Savannah Republican on Feb. 8, 1859, by the slave dealer Joseph Bryan for a two-day auction that became the largest in history. Four hundred thirty-six men, women and children were sold for $303,850, equivalent to about $9.4 million today.

Again and again, delving into each site, you find it to be a window into unspeakable suffering but also unimaginable resilience. Next to the I-95 highway in Richmond, there’s a fenced-in area that for about 20 years starting in the mid-1840s was home to a compound owned by the slave trader Robert Lumpkin. Called Lumpkin’s Jail, it included a pen to hold enslaved people — many of them fugitives — before they were sold in auctions and private sales on the property. The site, one of the few in the country that are marked, is part of a self-guided slavery tour in Richmond. The tour runs through the downtown area called Shockoe Bottom, where auction houses were concentrated. But you could walk through Shockoe Bottom today, a hub of restaurants, clubs and small businesses, and remain completely unaware of this history.

One person held at Lumpkin’s Jail was Anthony Burns, an enslaved person in Richmond who stowed away on a ship in 1854, escaping to Boston. When he was captured shortly after, thousands of local abolitionists tried to prevent him from being re-enslaved, but the courts ordered Burns returned to Virginia, where he was soon jailed in a small cell in Lumpkin’s Jail, painfully manacled much of the time. “The grip of the irons impeded the circulation of his blood, made hot and rapid by the stifling atmosphere, and caused his feet to swell enormously,” reports his biographer, Charles Emery Stevens. Burns was kept in this jail for four months until he was purchased there by a plantation owner from North Carolina. But he had not been forgotten by a black congregation and other abolitionists in Boston, who purchased his freedom. He went on to study at Oberlin College and spent his final years in Canada as a Baptist preacher.

Even well-known sites of slave labor look different when seen through the lens of the auction. When Thomas Jefferson died, on July 4, 1826, the enslaved people he owned at Monticello suddenly faced a perilous future. Jefferson’s will freed only five of them, including two children he fathered with Sally Hemings, an enslaved woman at his Monticello plantation. But Jefferson had many debts, and to pay them off, his executors sold 133 people, scattering them across the country. The first auction was held in 1827, most likely on or near the West Portico steps of the mansion; another followed two years later at the Eagle Tavern, in downtown Charlottesville.

Peter Fossett, 11, was among the people sold. His father, Joseph Fossett, had been Monticello’s blacksmith, freed by Jefferson in his will. Although Joseph was able to emancipate much of his family, he was unable to secure freedom for Peter. Peter was purchased by Col. John Jones and unsuccessfully tried to run away twice. In 1850 he was once again put on the auction block, but this time, friends and family were able to purchase his freedom, and 23 years after first being separated from them, Peter finally rejoined his family in Ohio, where they had settled. He went on to become an ordained minister and a conductor on the Underground Railroad.

Some 400,000 people visit Monticello every year, inspired, in part, by Jefferson’s legacy as a founding father and promoter of freedom. They take photographs and stroll up and down the famous West Portico steps — the image depicted on the United States nickel since 1938. Until they come, visitors most likely have not imagined a slave auction taking place on the property, let alone on those famous stairs. Perhaps Jefferson’s greatest contribution is not the realization of freedom for all but the creation of a blueprint for future generations to follow. Spurred on by the pioneering research of Annette Gordon-Reed, Lucia Stanton, Niya Bates and others, Monticello has more fully acknowledged Thomas Jefferson’s legacy as not just the writer of the Declaration of Independence but also an enslaver. At his plantation, the auctions are described in an exhibit, but in downtown Charlottesville, where the second occurred, there is no specific mention of the auction.

An advertisement that appeared in The Charlottesville Central Gazette on Jan. 15, 1827, for the sale of Thomas Jefferson’s enslaved workers. One hundred people were sold that day.

The lack of physical markers is just one obstacle to reclaiming the history of America’s slave-sale sites. Quite a few happened in places, including in Northern states, that the general public may not typically associate with slavery. On Main Street in East Brunswick, N.J., for example, a power station now stands on a site that previously was part of the estate of Jacob Van Wickle — a judge in Middlesex County who, along with a few collaborators, perpetrated one of the most infamous slave-selling schemes in the state’s history, selling off some 100 enslaved people in 1818.

At the time, New Jersey was moving to end slavery. State law held that children born to an enslaved woman were free, but had to remain in service to their mothers’ owners until they became adults. There were two loopholes, however. First, if their mothers were sold, their own enslavement could be temporarily extended; second, enslaved people could be moved from the state and remain enslaved, so long as they gave their consent. Van Wickle used these loopholes with cruel effectiveness. He and his collaborators often signed off on paperwork that moved unwitting people, including mothers and their freeborn children, to the South. Then he sold them to traders and planters in Louisiana, separating them from their families — most of whom would never see them again. Though there was local outcry when his dealings were discovered, he himself was never punished for his crimes.

An 1852 photograph of men in front of the slave pens of Bernard Lynch, who ran one of the largest slave markets in St. Louis.

Even though the story of Van Wickle and his slave ring was reported in newspapers at the time and has since been chronicled by historians like James Gigantino, many present-day residents of the area were not aware of many of the story’s details. But when the Rev. Karen G. Johnston at the Unitarian Society in East Brunswick learned about it a few years ago, she decided that something had to be done to acknowledge the pain and suffering of those who were sold away. Two years ago, members of the church, as well as the local N.A.A.C.P., the New Jersey chapter of the Afro-American Historical and Genealogical Society and others, formed the Lost Souls Public Memorial Project, which is developing teaching resources for local schools and is raising funds for a permanent memorial. On May 25, 2018, members of the project gathered in a solemn ceremony to read the names of people Van Wickle sold into slavery. The names included: Claresse and her son Hercules; Florah and her daughter Susan; Hager and her three children, Roda, Mary and Augustus. “I believe by remembering these lost souls back into our community,” Johnston told those who had gathered, “that that is a healing act.”

More than a century and a half after Emancipation, there remains much more healing to be done, in part because America has yet to adequately memorialize slavery. At the new Smithsonian National Museum of African-Amerian History and Culture, an entire floor is dedicated to the slave trade and slavery; through the United States National Park Service, we have the National Underground Railroad Network to Freedom and the Harriet Tubman Home, which honor and preserve the resistance to slavery. There are some restored plantations, like the Whitney in Louisiana, that conduct excellent slavery tours. But sites of African-American focus currently represent just 2 percent of those registered on the National Register of Historic Places, and only a portion of those are devoted to slavery — even as some 1,800 monuments to the Confederacy still exist all across the country, an inequality that mirrors the social injustices that have haunted this country since its founding.

How can we create a more equitable map of American history? One clear way to do it would be to provide a fuller accounting of our shared past, one that gives voice to the experience of the enslaved and ensures that their experience will never be forgotten. To look at some of these images, which show former slave-sale sites in the present day, is to grasp how invisible some of American history’s most grievous wounds have become. If we were to mark all these sites for posterity, we would help to heal their dark legacy, in much the same way that 19th-century abolitionists, both black and white, depicted the trauma of enslaved Africans on the auction block in their art and literature. By foregrounding the image of an enslaved mother torn from her infant, those abolitionists reminded the public of the horror of slavery and helped influence the course of history. Their insistence on telling these stories helped America live up to its ideals and made it a more demo­cratic country. Perhaps marking these sites could do the same.