This was a practiced line, but also an earnest form of self-indictment: Cummings’s way of admitting his own ignorance on the subject of slavery and its legacy, and by extension encouraging visitors to confront their own. As with the rest of his real estate portfolio, which includes miles of raw countryside and swampland, a 12-story luxury hotel near the French Quarter, a cattle farm in rural Mississippi and a 1,200-acre ranch in West Texas that he has never set foot on, he initially gravitated toward the Whitney simply because it was for sale. (“Whatever Uncle Sam and the bartender let me keep,” he likes to note, “I bought real estate with it.”) Originally built by the Haydel family, a prosperous clan of German immigrants who ran the property from 1752 to 1867, the grounds had been uninhabited for a quarter century. “I knew I wasn’t going to live here,” Cummings said as he drove past the blacksmith’s shop that he spent $300,000 rebuilding, where a plaque noted that a slave named Robin worked on the plantation for 40 years and where the actor Jamie Foxx, playing a slave in “Django Unchained,” was filmed being branded. “But aside from that, I didn’t know what I would do with the place.”

It takes just a few minutes of conversation with Cummings, however, to understand that he would never have been keen on restoring the Whitney in the mold of neighboring plantations, which rely on weddings and sorority reunions to supplement the income brought in by picnicking tourists. Pet projects he has taken up in recent years include outlining for the Vatican a list of wrongs the Catholic Church should formally apologize for and — to the chagrin of, in his words, “my friends who have all had political sex changes in the past 15 years” — exploring ways to curb the influence of conservative “super PACs.” Decades ago, his interest in abuses of power led to his involvement in the civil rights movement; in 1968, he worked alongside African-American activists to get the Audubon Park swimming pool in New Orleans opened to blacks. “If someone is going to deny someone rights simply because they have the power to do it — well, I’m interested,” he explained. “I’m coming, and I’m going to bring the cannons.”

Still, his plans for the Whitney might have gone in an entirely different direction, if not for the existence of an unlikely document. The property’s previous owner was Formosa, a plastics and petrochemical giant, which in 1991 planned to build a $700 million plant for manufacturing rayon on its nearly 2,000 acres. Preservationists and environmentalists balked. Looking for avenues of appeasement, Formosa commissioned an exhaustive survey of the grounds, with the idea that the most historic sections would be turned into a token museum of Creole culture while a majority of the rest would be razed to make way for the factory. In the end, it was wasted money and effort: The opposition remained vigilant, rayon was going out of fashion, the Whitney went back on the market and Cummings inherited the eight-volume study with the purchase. “Thanks to Formosa, I knew more about my plantation than anyone else around here — maybe more than any plantation in America outside of Monticello,” said Cummings, a litigator accustomed to teasing secrets from dense paperwork. “A lot of what was in there was about the architecture and artifacts, but you started to see the story of slavery. You saw it in terms of who built what.”

After digesting the study, Cummings began reading “any book I could find” about slavery. Particularly influential was “Africans in Colonial Louisiana,” by Gwendolyn Midlo Hall, a professor at Rutgers. Certain details startled Cummings, like the fact that 38 percent of slaves shipped from Africa ended up in Brazil. No wonder, he thought, that the women he watched on television celebrating Carnival in Rio de Janeiro so closely resembled those he saw dancing in the Mardi Gras parades that surrounded him as a youth. “I started to see slavery and the hangover from slavery everywhere I looked,” he said. As a descendant of Irish laborers, he has no direct ties to slaveholders; still, in a departure from the views held by many Southern whites, Cummings considered the issue a personal one. “If ‘guilt’ is the best word to use, then yes, I feel guilt,” he said. “I mean, you start understanding that the wealth of this part of the world — wealth that has benefited me — was created by some half a million black people who just passed us by. How is it that we don’t acknowledge this?”

Cummings steered the vehicle past the yellowing fronds of banana trees and pulled to a stop in front of a sculpture, a black angel embracing a dead infant, the centerpiece of a memorial honoring the 2,200 enslaved children who died in the parish in the 40 years leading up to the Emancipation Proclamation of 1863. At traditional museums, such memorials come to fruition only after a lengthy process — proposals by artists, debates among the board members, the securing of funds. This statue, though, like everything on the property, began as a vision in Cummings’s mind and became a reality shortly after he pulled out his checkbook. Perhaps most remarkable is that this unconventional model has yielded conventionally effective results: at once chastening and challenging, beautiful and haunting. “Everything about the way the place came together says that it shouldn’t work,” says Laura Rosanne Adderley, a Tulane history professor specializing in slavery who has visited the Whitney twice since it opened. “And yet for the most part it does, superbly and even radically. Like Maya Lin’s memorial, the Whitney has figured out a way to mourn those we as a society are often reluctant to mourn.”

Before leaving the grounds, Cummings stopped at the edge of the property’s small lagoon. It was here that the Whitney’s most provocative memorial would soon be completed, one dedicated to the victims of the German Coast Uprising, an event rarely mentioned in American history books. In January 1811, at least 125 slaves walked off their plantations and, dressed in makeshift military garb, began marching in revolt along River Road toward New Orleans. (The area was then called the German Coast for the high number of German immigrants, like the Haydels.) The slaves were suppressed by militias after two days, with about 95 killed, some during fighting and some after the show trials that followed. As a warning to other slaves, dozens were decapitated, their heads placed on spikes along River Road and in what is now Jackson Square in the French Quarter.