The historian Marcus Rediker opens “The Slave Ship: A Human History” with a harrowing reconstruction of the journey, for a captive, from shore to ship:
An estimated 12.5 million people endured some version of this journey, captured and shipped mainly from the western coast of Africa to the Western Hemisphere during the four centuries of the trans-Atlantic slave trade. Of that number, about 10.7 million survived to reach the shores of the so-called New World.
It is thanks to decades of painstaking, difficult work that we know a great deal about the scale of human trafficking across the Atlantic Ocean and about the people aboard each ship. Much of that research is available to the public in the form of the SlaveVoyages database. A detailed repository of information on individual ships, individual voyages and even individual people, it is a groundbreaking tool for scholars of slavery, the slave trade and the Atlantic world. And it continues to grow. Last year, the team behind SlaveVoyages introduced a new data set with information on the domestic slave trade within the United States, titled “Oceans of Kinfolk.”
The systematic effort to quantify the slave trade goes back at least as far as the nineteenth century. For example, in the 1888 edition of the second volume of his “History of the United States of America, from the Discovery of the American Continent,” the historian George Bancroft estimates that “the number of negroes” imported by “the English into the Spanish, French, and English West Indies, and the English continental colonies, to have been, collectively, nearly three millions: to which are to be added more than a quarter of a million purchased in Africa, and thrown into the Atlantic on passage.” He adds, later, that “After every deduction, the trade retains its gigantic character of crime.”
In 1958, the historians Alfred H. Conrad and John R. Meyer transformed the study of slavery — and of economic history more broadly — with the publication of “The Economics of Slavery in the Ante Bellum South.” Their methods, which relied on statistical data and mathematical analysis, revolutionized the field.
The origins of SlaveVoyages lie in this period and, specifically, in the work of a group of scholars who, a decade later, began to collect data on slave-trading voyages and encode it for use with a mainframe computer.
“It goes back to the late 1960s and the work of Philip Curtin,” David Eltis, an emeritus professor of history at Emory and a former co-editor of the SlaveVoyages database, told me. “He did this book called ‘The Atlantic Slave Trade: A Census,’ part of which involved computerizing — which was quite a dramatic step in those days — a list of slave voyages for the 19th century. And he sent me, in response to a cold call, a box of two thousand three-hundred and thirteen IBM cards, one card for each voyage. And that was the starting point.”
Over the next two decades, working independently and collaboratively, historians in the United States and around the world would turn this archival information on the trans-Atlantic trade into data sets representing more than 11,000 individual voyages, a significant accomplishment even if it represented only a fraction of the trade in human lives from the 15th century to its end in the 19th century.
Later, beginning in the 1990s, those scholars began to integrate this data — which encompassed the British, Dutch, French and Portuguese slave trade — into a single data set. By the end of the decade, the first SlaveVoyages database had been released to the public as an (expensive) CD-ROM set including details from more than 27,000 voyages.
It is hard to exaggerate the significance of this work for historians of slavery and the slave trade. An arrival to and departure from port tells a story. To know when, where and how many times a ship disembarked is to know a little more about the nature of the specific exchange as well as the slave trade as a whole. Every bit of new information fills in the blanks of a time that has long since passed out of living memory.
After nearly 10 years as physical media, SlaveVoyages was introduced to the public as a website in 2008 and then relaunched in 2019 with a new interface and even more detail. As it stands today, the site, funded primarily by grants, contains data sets on various aspects of the slave trade: a database on the trans-Atlantic trade with more than 36,000 entries, a database containing entries on voyages that took place within the Americas and a database with the personal details of more than 95,000 enslaved Africans found on these ships.
The newest addition to SlaveVoyages is a data set that documents the “coastwise” traffic to New Orleans during the antebellum years of 1820 to 1860, when it was the largest slave-trading market in the country. The 1807 law that forbade the importation of enslaved Africans to the United States also required any captain of a coastwise vessel with enslaved people on board to file, at departure and on arrival, a manifest listing those individuals by name.
Countless enslaved Africans arrived at ports up and down the coast of the United States, but the largest share were sent to New Orleans. This new data set draws from roughly 4,000 “slave manifests” to document the traffic to that port. Those manifests list more than 63,000 captives, including names and physical descriptions, as well as information on an individual’s owner and information on the vessel and its captain.
Because of its specificity with regard to individual enslaved people, this new information is as pathbreaking for lay researchers and genealogists as it is for scholars and historians. It is also, for me, an opportunity to think about the difficult ethical questions that surround this work: How exactly do we relate to data that allows someone — anyone — to identify a specific enslaved person? How do we wield these powerful tools for quantitative analysis without abstracting the human reality away from the story? And what does it mean to study something as wicked and monstrous as the slave trade using some of the tools of the trade itself?
Before we go any further, it is worth spending a little more time with the history of the trans-Atlantic slave trade itself, at least as it relates to the United States.
A large majority of people taken from Africa were sold to enslavers in either South America or the Caribbean. British, Dutch, French, Spanish and Portuguese traders brought their captives to, among other places, modern-day Jamaica, Barbados, Cuba, Puerto Rico, Brazil and Haiti, as well as Argentina, Antigua and the Bahamas. A little over 3.5 percent of the total, about 389,000 people, arrived on the shores of British North America and the Gulf Coast during those centuries when slave ships could find port.
In the last decades of the 18th century, moral and religious activism fueled an effort to suppress British involvement in the African slave trade. In 1774, the Continental Congress of rebelling American states adopted a temporary general nonimportation policy against Britain and its possessions, effectively halting the slave trade, although the policy lapsed under the Confederation Congress in the wake of the Revolutionary War. Still, by 1787, most of the states of the newly independent United States had banned the importation of slaves, although slavery itself continued to thrive in the southeastern part of the country.
From 1787 to 1788, Americans would write and ratify a new Constitution that, in a concession to Lower South planters who demanded access to the trans-Atlantic trade, forbade a ban on the foreign slave trade for at least the next 20 years. But Congress could — and, in 1794, did — prohibit American ships from participating. In 1807, right on schedule, Congress passed — and President Thomas Jefferson, a slave-owning Virginian, signed — a measure to abolish the importation of enslaved Africans to the United States, effective Jan. 1, 1808.
But the end to American involvement in the trans-Atlantic slave trade (or at least the official end, given an illegal trade that would not end until the start of the Civil War) did not mean the end of the slave trade altogether. Slavery remained a big and booming business, driven by demand for tobacco, rice, indigo and increasingly cotton, which was already on its path to dominance as the principal cash crop of the slaveholding South.
Within a decade of the invention of the cotton gin in 1793, annual cotton production had grown twentyfold to 35 million pounds in 1800. By 1810, production had risen to roughly 85 million pounds per year, accounting for more than 20 percent of the nation’s export revenue. By 1820, the United States was producing something in the area of 160 million pounds of cotton a year.
Fueling this growth was the rapid expansion of American territory, facilitated by events abroad. In August 1791, the Haitian Revolution began with an insurrection of enslaved people. In 1803, Haitian revolutionaries defeated a final French Army expedition sent to pacify the colony after years of bloody conflict. To pay for this expensive quagmire — and to keep the territory out of the hands of the British — the soon-to-be-emperor Napoleon Bonaparte sold what remained of French North America to the United States at a fire-sale price.
The new territory nearly doubled the size of the country, opening new land to settlement and commercial cultivation. And as the American nation expanded further into the southeast, so too did its slave system. Planters moved from east to west. Some brought slaves. Others needed to buy them. There had always been an internal market for enslaved labor, but the end of the international trade made it larger and more lucrative.
It is hard to quantify the total volume of sales on the domestic slave trade, but scholars estimate that in the 40-year period between the Missouri Compromise and the secession crisis, at least 875,000 people were sent south and southwest from the Upper South, most as a result of commercial transactions, the rest as a consequence of planter migration.
New, more granular data on voyages and migrations and sales will help scholars delve deeper than ever into the nature of slavery in the United States, into specifics of the trade and into the ways it shaped the political economy of the American republic.
But no data, no matter how precise, is complete. There are things that quantification can obscure. And there are, again, ethical questions that must be asked and answered when dealing with the quantitative study of human atrocity, which is what we’re ultimately doing when we bring statistical and mathematical methods to the study of slavery.
To think about the slave trade in terms of vessels and voyages — to look at it as columns in a spreadsheet or as points in an online animation — is to engage in an act of abstraction. Historians have no choice but to rely, as Marcus Rediker writes, on “ledgers and almanacs, balance sheets, graphs and tables.” But it carries a heavy cost, dehumanizing a reality that, he writes, “must, for moral and political reasons, be understood concretely.”
Consider, as well, the extent to which the tools of abstraction are themselves tied up in the history of the trans-Atlantic slave trade. As the historian Jennifer L. Morgan notes in “Reckoning With Slavery: Gender, Kinship, and Capitalism in the Early Black Atlantic,” the fathers of modern demography, the 17th-century English writers and mathematicians William Petty and John Graunt, were “thinking through problems of population and mobility at precisely the moment when England had solidified its commitment to the slave trade.”
Their questions were ones of statecraft: How could England increase its wealth? How could it handle its surplus population? And what would it do with “excessive populations that did not consume” in the formal market? Petty was concerned with Ireland — Britain’s first colony, of sorts — and the Irish. He thought that if they could be forcibly transferred to England, then they could, in Morgan’s words, become “something valuable because of their ability to augment the population and labor power of the English.”
This conceptual breakthrough, Morgan told me in an interview, cannot be disentangled from the slave trade. The English, she said, “are learning to think about people as ‘abstractable.’ By watching what the Spanish and what the Portuguese have been doing for 200 years, but also by doing it themselves, saying, ‘Oh, I can take Africans from here and move them to there, and then I can use them for my own purposes.’”
Embedded in this early project of quantification — Morgan notes in her book that Graunt “mounted what historians and political scientists agree was the first systematic use of demographic evidence to understand a contemporary sociopolitical problem” — is an objectification of human life.
Compounding these problems is the extent to which we rely on the documentation of slaveholders for our knowledge of the enslaved.
Writing of enslaved women on Barbados, the historian Marisa J. Fuentes notes in “Dispossessed Lives: Enslaved Women, Violence, and the Archive” that “they appear as historical subjects through the form and content of archival documents in the manner in which they lived: spectacularly violated, objectified, disposable, hypersexualized, and silenced. The violence is transferred from the enslaved bodies to the documents that count, condemn, assess, and evoke them, and we receive them in this condition.”
She continues: “Epistemic violence originates from the knowledge produced about enslaved women by white men and women in this society, and that knowledge is what survives in archival form.”
The traders, enslavers, officials and others who documented the slave trade did so in the context of legal and commercial relationships. For them, the enslaved were objects to be bought and sold for profit, wealth and status. If an individual’s “historical” life is shaped by the documents and images they leave behind, then, as Fuentes writes, most enslaved women, men and children live (and have lived) their historical lives as “numbers on an estate inventory or a ship’s ledger.” It is in that form that they are then shaped by “additional commodification” — used but not necessarily understood as having been fully alive.
“The data that we have about those ships is also kind of caught in a stranglehold of ship captains who care about some things and don’t care about others,” Jennifer Morgan said. We know what was important to them. It is the task of the historian to bring other resources to bear on this knowledge, to shed light on what the documents, and the data, might obscure.
“By merely reproducing the metrics of slave traders,” Fuentes said, “you’re not actually providing us with information about the people, the humans, who actually bore the brunt of this violence. And that’s important. It is important to humanize this history, to understand that this happened to African human beings.”
It’s here that we must engage with the question of the public. Work like the SlaveVoyages database exists in the “digital humanities,” a frequently public-facing realm of scholarship and inquiry. And within that context, an important part of respecting the humanity of the enslaved is thinking about their descendants.
“If you’re doing a digital humanities project, it exists in the world,” said Jessica Marie Johnson, an assistant professor of history at Johns Hopkins and the author of “Wicked Flesh: Black Women, Intimacy, and Freedom in the Atlantic World.” “It exists among a public that is beyond the academy and beyond Silicon Valley. And that means that there should be certain other questions that we ask, a different kind of ethics of care and a different morality that we bring to things.”
I have some personal experience with this. Years ago, I worked with colleagues at Slate magazine on an infographic that showed the scale and duration of the trans-Atlantic slave trade, using data from the SlaveVoyages website. Plotted on a map of the Atlantic Ocean, it represented each ship as a single dot, moving from its departure point on the African coast to its arrival point in the Americas. As time goes on — as the 16th century becomes the 17th century becomes the 18th century becomes the 19th century — the dots grow overwhelming.
What I did not appreciate at the time was how we, the creators, would lose control of our creation. People encountered the infographic in ways we could not anticipate and that lay outside of our imagination. It was repurposed for schools and museums, used for personal projects and in exhibitions. Inevitably, some of these people would contact us. They would want to know more: about the ships, about the journeys, about the people. And we couldn’t answer them.
When I think back to the creation of that infographic, I wonder whether we had shown the care demanded of the data. Whether we had, in creating this abstraction, re-enacted — however inadvertently — some of the objectification of the slave trade.
One way to address this problem is to ensure that the audience understands the context. “I want to make sure that Black people in the audience feel like they are not being assaulted again by the information in the project or by the methods behind the project or any of that,” Johnson said, speaking of SlaveVoyages and other public work around slavery. “Everything from the colors on a website to the metadata itself is reshaped if we decide that the people in the audience should not feel harmed” and “should not be re-assaulted by their experience in this project or on this site.”
The new addition to SlaveVoyages, “Oceans of Kinfolk,” was made with these questions and concerns in mind. “You can use quantitative methodologies to learn about enslaved people, to learn about their experience,” said Jennie Williams, who collected and compiled the data as a doctoral student at Johns Hopkins and helped integrate it into the database as a postdoctoral research fellow at the University of California, Santa Cruz. Williams is also a friend, with whom I have discussed this work for years.
The slave traders who documented their cargo for federal authorities — producing the manifests that were the foundation of Williams’s work — were obviously not interested in the lives and experiences of their captives, except as cargo. They had no intention of preserving their identities as people. But despite this indifference, Williams said, that is essentially what happened.
These records are unique, Williams explained. If you look at bills of sale, she said, “most people are not identified by last name. If you look at fugitive ads, which I looked at 11,000 of and did a comparison with the manifests, which is also my dissertation, most people are not listed by last name. That is because slaveholders did not recognize enslaved people’s last names. They knew they had last names — they did not care.”
But, she continued: “If you asked an enslaved person ‘what is your name,’ they responded with a first and last name much more commonly than you would see in the other records. And so, manifests, compared to all other records of enslaved people I’ve seen, have a much higher proportion of last names in them.”
That fact makes this data important for genealogists and others interested in their family histories. “If Black families are able to reach or to trace their genealogy back to the 19th century, they very rarely get past 1870,” the year of the first federal census after slavery, Williams said. “This is not a database of everybody, but if I can get people to know about it, it is potentially useful for millions of people, because 63,000 people have millions of descendants.”
David Eltis concurred. “It’s quite rare to have this big body or big cache of names for enslaved people in the United States,” he said. “A person can go back and find something from the early 19th century, find a person with a possible connection. And that is simply not possible for the trans-Atlantic material. You can’t go back to Africa.”
If part of the ethical task for quantitative researchers of slavery is to preserve the humanity of the enslaved despite the nature of the sources, then connecting this data to Black genealogists is one way to underscore the fact that these were real people with real legacies.
“I could barely sleep the first night,” said Carlton Houston, a descendant of one of the 63,000 captives listed as part of the coastal trade to New Orleans, speaking of when he first saw the document listing his ancestor Simon Wilson, a young man sold for the purpose of “breeding” more people. “It was so compelling to see. Here’s the manifest, here’s this name, to have this visual in your head of these young people, chained on a boat, not really knowing where they were going.”
“There was not much for him to look forward to, you know, just this abysmal world that they lived in,” Houston added. “And yet, they survived, and didn’t give up.”
As for the sources themselves, it may be possible to use their physicality — the fact that these ledger books, bills of sale and fugitive slave ads are real, tangible objects — to tell stories about the humans involved in this centuries-long nightmare, to use the means of objectifying others to undermine the objectification itself.
“There is a strange way in which the everydayness of the document helps you understand the extraordinary imbalance of power and the wrongness,” Walter Johnson, a professor of history and African and African American studies at Harvard, said. “If somebody smudges the ink on a ledger, you have to imagine a person writing that. And once you imagine a person writing that, you’re imagining the extraordinary power that those words on a page have over somebody’s life. That somebody’s life and their lineage is actually being conveyed by that errant pen stroke. And then that takes you to a moment where you have to imagine those people.”
Indeed, the very banality of this material can help us understand how this system survived, and thrived, for so long. “I am not a historian of slavery because I want to spend my time understanding massive moments of spectacular violence,” Jennifer Morgan told me. “I actually want to understand tiny moments of violence, because that’s what I see as adding up to a kind of numbness — a numbness of empathy, a numbness to human interconnection.”
All of this is to say that with the history of slavery, the quantitative and the qualitative must inform each other. It is important to know the size and scale of the slave trade, of the way it was standardized and institutionalized, of the way it shaped the history of the entire Atlantic world.
But as every historian I spoke to for this story emphasized, it is also vital that we have an intimate understanding of the people who were part of this story and specifically of the people who were forced into it. It is for good reason that W.E.B. Du Bois once called the trans-Atlantic slave trade “the most magnificent drama in the last thousand years of human history”; a tragedy that involved “the transportation of 10 million human beings out of the dark beauty of their mother continent into the newfound Eldorado of the West” where they “descended into Hell”; and an “upheaval of humanity like the Reformation and the French Revolution.”
The future of SlaveVoyages will include even more information on the people involved in the slave trade, enslaved and enslavers alike. “We would like to add an intra-African slave trade database because there is a lot of movement of enslaved people on the eastern side of the Atlantic,” David Eltis said. He also told me that he can imagine a merger with scholars documenting the slave trade across the Indian Ocean, the roots of which go back to antiquity and whose more modern form was concurrent with the trans-Atlantic trade. “We’re really leaning into territory which was unimaginable back in 1969,” he said.
We may not have many statues of the enslaved — we may not have anywhere near enough letters and portraits and personal records for the millions who lived and died in bondage — but they were living, breathing individuals nonetheless, as real to the world as the men and women we put on pedestals.
As we learn from new data and new methods, it is paramount that we keep the truth of their essential humanity at the forefront of our efforts. We must have awareness, care and respect, lest we recapitulate the objectification of the slave trade itself. It is possible, after all, to disturb a grave without ever touching the soil.
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