In August 1518, King Charles I authorized Spain to ship enslaved people directly from Africa to the Americas. The edict marked a new phase in the transatlantic slave trade in which the numbers of enslaved people brought directly to the Americas—without going through a European port first—rose dramatically.

Researchers have uncovered new details about those first direct voyages.

Historians David Wheat and Marc Eagle have identified about 18 direct voyages from Africa to the Americas in the first several years after Charles I authorized these trips—the earliest such voyages we know about.

The transatlantic slave trade didn’t start in 1518, but it did increase after King Charles authorized direct Africa-to-Caribbean trips that year. In the 1510s and ‘20s, ships sailing from Spain to the Caribbean settlements of Puerto Rico and Hispaniola might contain as few as one or two enslaved people, or as many as 30 or 40.

“By the mid 1520s, we’re seeing 200—sometimes as many as almost 300—captives being brought on the same slave ship [from Africa],” says Wheat, a history professor at Michigan State University. It’s difficult to trace what parts of Africa the captives on board came from, since many were captured on the mainland and shipped to island ports off the coast before Spanish boats took them to the Americas.

“This is also some of our earliest examples of enslaved people throwing themselves overboard, people dying of malnutrition,” Wheat adds. “Some of the same really horrible and violent and brutal aspects of the slave trade that was seen much later on, we’re seeing them already in these voyages from São Tomé in the 1520s.”

São Tomé was a colonial island port off the west coast of Africa that Portugal established in the mid-1400s. Before 1518, Portugal forced enslaved Africans to work on islands in the eastern Atlantic. In addition, Spanish ships brought captive Africans to the Iberian Peninsula, from which they sent some to the Caribbean.

Spain may have increased the number of enslaved Africans it brought to the Caribbean after 1518 because the Native people it had previously enslaved there were dying from European disease and colonial violence. Though it’s not clear how many captive Africans arrived through the 1520s, Wheat estimates the number is in the thousands.

We don’t have many firsthand accounts of Africans in the Americas during this period, but one exception is Rodrigo Lopez, a former enslaved man in Africa’s Cape Verde islands freed in a slaveholder’s will. After he became a free man, he was captured and sent to the Americas, where he was re-enslaved in the late 1520s. Lopez, who could read and write Latin, protested his re-enslavement and won back his freedom in the early ’30s.

“It’s an unusual case because we have not only a person who was of very high status among enslaved people in the Cape Verde islands,” Wheat says, but also because “he sues for his freedom and he writes about it, and that document still survives.” Lopez explained that one of his master’s former employees kidnapped him in the night and sold him into slavery. This was illegal, Lopez argued, because he was free man now.

Most of the enslaved men, women and children in the Caribbean didn’t have the option of suing for their freedom. Still, there were some free people of color in Spanish-American colonies, because race wasn’t yet as closely tied to slave status as it would be during American chattel slavery.

“It was considered normal for enslaved people to be black, even though there were enslaved people of other origins,” Wheat says. “But at the same time, it was also normal for there to be small numbers of free people of color in Iberian societies around the Atlantic.”

Wheat and Eagle will publish an essay on their research in a forthcoming book, From the Galleons to the Highlands: Slave Trade Routes in the Spanish Americas in 2019_._ For the project, they spent a lot of time studying Spanish shipping records and lawsuits from the Caribbean that mentioned slave voyages.

“Most of [the lawsuits] involve either one of two things…corruption or disgruntled investors,” Wheat says. Corruption often involved “officials who had permitted unlicensed slave trading voyages to take place.” Crown officials pursued these types of corruption lawsuits, whereas investors usually sued after losing money on a slave voyage.

Dealing with the “casual brutality” in these records is often difficult, says Eagle, a history professor at Western Kentucky University. Even in a report about a slave revolt, “the whole report is about a captain who’s trying to justify the fact that he’s lost some goods to his investors, and it really is just like he’s talking about merchandise,” he observes.

“When a slaves dies they’ll send somebody to [record] what the brand was on the slave and what they died of and keep a record, and that’s all again for commercial purposes—they can claim that as loss later on,” Eagle continues. “So it is really kind of horrifying to read things like this and realize they’re talking about human beings.”