BOSTON — A Harvard University professor on Tuesday unveiled a fourth-century fragment of papyrus she said is the only existing ancient text quoting Jesus explicitly referring to having a wife.

Karen King, an expert in the history of Christianity, said the text contains a dialogue in which Jesus refers to “my wife,” whom he identifies as Mary. King says the fragment of Coptic script is a copy of a gospel, probably written in Greek in the second century.

King unveiled the tiny fragment at a conference of Coptic experts in Rome. She said it doesn’t prove Jesus was married but speaks to issues of family and marriage that faced Christians.

Four words in the 1.5-by-3-inch fragment provide the first evidence that some early Christians believed Jesus had been married, King said. Those words, written in a language of ancient Egyptian Christians, translate to “Jesus said to them, my wife,” King said.

King said that in the dialogue the disciples discuss whether Mary is worthy and Jesus says “she can be my disciple.”

Christian tradition has long held that Jesus was unmarried even though there was no reliable historical evidence to support that, King said. The new gospel, she said, “tells us that the whole question only came up as part of vociferous debates about sexuality and marriage.”

“From the very beginning, Christians disagreed about whether it was better not to marry,” she said, “but it was over a century after Jesus’s death before they began appealing to Jesus’s marital status to support their positions.”

The fragment belongs to an anonymous private collector who contacted King to help translate it.

The unclear origins of the document should encourage people to be cautious, said Bible scholar Ben Witherington III, a professor and author who teaches at Asbury Theological Seminary in Wilmore, Ky. He said the document follows the pattern of Gnostic texts of the second, third and fourth centuries, using “the language of intimacy to talk about spiritual relationships.”

“What we hear from the Gnostic is this practice called the sister-wife texts, where they carried around a female believer with them who cooks for them and cleans for them and does the usual domestic chores, but they have no sexual relationship whatsoever” during the strong monastic periods of the third and fourth centuries, Witherington said. “In other words, this is no confirmation of the Da Vinci Code or even of the idea that the Gnostics thought Jesus was married in the normal sense of the word.”