Daniella Santoro and her husband, Aaron Lorenz, were busy “de-junglefying” the backyard of their New Orleans home in March when they found something, well, curious.

There in the dirt and muck, covered by thick vines, was a marble slab with Latin engraving.

Dr. Santoro, an anthropologist, thought that the stone looked like a grave marker, but there was no English anywhere on it.

It turns out that Dr. Santoro was correct. The object was in fact a gravestone, but not for someone buried in her yard. No, the nearly 2,000-year-old grave marker belonged to a man named Sextus Congenius Verus, a second-century Roman sailor and soldier.

“I just was so sort of flabbergasted,” Dr. Santoro said in an interview on Friday. “I was just so surprised by the fact that it was actually real. How did it get here?”

The slab’s unearthing touched off a mystery that stretched across time and continents before finally, at least partly, being solved this week.

Susann Lusnia, an associate professor of classical studies at Tulane University, quickly identified and authenticated the tablet after Dr. Santoro emailed her a picture of it. When she first saw the picture, she said, “it was like a shiver up my spine.”

“It was clear to me that it was an ancient Roman inscription,” Professor Lusnia said. “I was going to be surprised if it turned out not to be, but I was also surprised that it was a Roman inscription because it’s in New Orleans and somebody’s backyard.”

Coincidentally, Professor Lusnia said, Dr. Santoro emailed her on April 1.

“Not that I was really skeptical,” she said, “but I just found that kind of amusing that it was on April Fools’ Day.”

Using key words and phrases, Professor Lusnia quickly figured out the tablet’s funerary purpose and recognized the inscription as one of several that were found in an ancient Roman cemetery in the 1860s in Civitavecchia, Italy.

The gravestone begins with the words: “To the spirits of the dead for Sextus Congenius Verus,” according to a translation provided by Professor Lusnia. It said that he had served in the military for 22 years and died at the age of 42. The marker was made for him by his heirs.

The tablet was in a municipal library in 1910, according to Professor Lusnia, and its text was recorded in the “Corpus Inscriptionum Latinarum,” a primary reference source for Latin inscriptions. Then, in 1918, the stone was recorded as being at the new Museo Civico in Civitavecchia, but the museum was basically destroyed by Allied bombing during World War II.

That’s where things get murky. The slab would be lost to time — until Dr. Santoro and her husband uncovered it this spring.

Back when the stone was laid, Civitavecchia, which is about an hour north of Rome by train, was called Centumcellae, Professor Lusnia said. It was an imperial port city that today serves as a busy cruise ship terminal.

Lara Anniboletti, the director of the National Archaeological Museum of Civitavecchia, said in a statement that the epigraph was first discovered in 1864 in the Roman sepulchral area of the classiarii, a necropolis dating back to the second and third centuries A.D., in the Prato del Turco area of Civitavecchia.

“The epigraphs of the Civitavecchia classiarii document how these sailors were often recruited from distant regions of the Empire,” she said, adding that the inscriptions the museum has in its possession will be displayed in a new exhibition there, “offering a glimpse into daily life two thousand years ago.”

“It is hoped that, thanks to the joint efforts of the FBI and the Italian Carabinieri Command for the Protection of Cultural Heritage, the inscription found in New Orleans will also be returned and displayed in the new museum halls,” Dr. Anniboletti said.

The F.B.I. did not immediately respond to a request for comment because of the government shutdown.

As to how the grave marker ended up in a backyard in New Orleans, the Preservation Resource Center of New Orleans said on Thursday that a woman had come forward that day and claimed responsibility for placing the stone in the yard 21 years ago. She said that she had inherited it from her grandparents, who preserved it in a display case.

The woman’s grandfather, according to the center, was a soldier who was stationed in Italy during World War II. It’s unclear how he came to have it.

D. Ryan Gray, an anthropologist and professor at the University of New Orleans who also helped with identifying the slab, said that although he and his colleagues often handle inquiries from people who find strange objects in their yard, “I knew pretty quickly that it was something different than what we usually get.”

“Based on the style of the inscription and the type of stone, it was pretty clear from the outset that it wasn’t a New Orleans tombstone,” he said.

Dr. Gray said the stone’s finding “opens up a window” into what was happening after World War II with these kinds of souvenirs.

“I think we’ll see more people who kind of look into family collections and say, ‘Oh well, what is that’ as a result of this,” he said.

Professor Lusnia said that the “importance of a funerary inscription for a Roman is that it keeps their name in the public eye.”

“Memory is the way you have an afterlife in the Roman world,” she said. “To be remembered is to exist beyond your regular lifetime.”

And in that, Sextus Congenius Verus’s heirs have succeeded, perhaps far greater than they ever could have imagined.