Islam has existed in North America for hundreds of years, ever since enslaved people captured in Africa brought their religion over. In the 1700s, an English translation of the Quran (or Koran) actually became a bestseller among Protestants in England and its American colonies. One of its readers was Thomas Jefferson.

Jefferson’s personal copy of the Quran drew attention in early 2019 when Rashida Tlaib, one of the first two Muslim women elected to Congress, announced she’d use it during her swearing-in ceremony (she later decided to use her own). It’s not the first time a member of Congress has been sworn in with the centuries-old Quran—Keith Ellison, the first Muslim Congressman, did so in 2007—yet its use highlights the long and complicated history of Islam in the U.S.

“The Quran gained a popular readership among Protestants both in England and in North America largely out of curiosity,” says Denise A. Spellberg, a history professor at the University of Texas at Austin and author of Thomas Jefferson’s Qu'ran: Islam and the Founders. “But also because people thought of the book as a book of law and a way to understand Muslims with whom they were interacting already pretty consistently, in the Ottoman Empire and in North Africa.”

When Jefferson bought his Quran as a law student in 1765, it was probably because of his interest in understanding Ottoman law. It may have also influenced his original intention for the the Virginia Statute of Religious Freedom to protect the right to worship for “the Jew and the Gentile, the Christian and Mahometan, the Hindoo, and infidel of every denomination,” as he wrote in his autobiography.

This professed religious tolerance was probably mostly theoretical for Jefferson. At the time, he and many other people of European descent likely weren’t aware of how far Islam extended into parts of Africa not controlled by the Ottoman Empire; which means that, ironically, they might not have realized that many enslaved people in North America held the very faith they were studying.

Jefferson’s Quran was a 1734 translation by a British lawyer named George Sale. It was the first direct translation of the Quran from Arabic to English (the only other English version was a translation of a French translation published in 1649), and would remain the definitive English translation of the Quran into the late 1800s. In his introduction, Sale wrote that the purpose of the book was to help Protestants understand the Quran so that they could argue against it

“Whatever use an impartial version of the Korân may be of in other respects,” he wrote, “it is absolutely necessary to undeceive those who, from the ignorant or unfair translations which have appeared, have entertained too favorable an opinion of the original, and also to enable us effectually to expose the imposture.”

Yet although Sale’s translation was theoretically a tool for missionary conversion, that wasn’t what English-speakers in Britain and North America used it for in Jefferson’s day. Protestants didn’t start traveling to Africa and the Middle East with the explicit purpose of converting Muslims until the late 19th century, Spellberg says_._

“It’s true that George Sale, who did the first translation directly from Arabic to English, was sponsored by an Anglican missionary society,” she says. But it’s appeal went beyond its value as a missionary tool. Christians in the 18th century understood the value of learning about Islam. “The version that Thomas Jefferson bought was really a bestseller"—even with Sale’s 200-page introduction.

Given its history, Tlaib and Ellison’s choice to use Jefferson’s Quran in their private swearing-in ceremonies carries a particular significance. “By using Jefferson’s Quran, they’re affirming the fact that Islam has a long history in the United States, and is in fact an American religion,” Spellberg says.