ROME (RNS) When Pope Francis cradled the small box said to contain nine bone fragments believed to be the mortal remains of St. Peter, the first pope, he fanned the flames of a long-standing debate over the authenticity of ancient church relics.

Most old churches in Italy contain some ancient relic, ranging from a glass tube said to hold the blood of St. Gennaro in Naples to a section of what is believed to be Jesus' umbilical cord in the Basilica of St. John of Lateran in Rome. Perhaps the most famous religious relic in Italy -- the Shroud of Turin, believed by many to be Jesus' burial cloth -- will go on display again in early 2015, and Turin Archbishop Cesare Nosiglia this week invited Pope Francis to attend its public debut.

But St. Peter's bones are of particular importance, since they are the very basis -- both architecturally and spiritually -- for Catholicism's most important church. And yet the bones were only discovered during a series of excavations in the 1940s, almost 1,900 years after Peter died, in either 64 or 67 A.D.

They were reportedly found underneath a fourth-century monument, built by the Emperor Constantine, next to (but not inside of) a small walled area marked, in Greek, reading "Petros eni" -- "Peter is here."

According to the writings of Margherita Guarducci, a scholar on Greek antiquities who died in 1999, one of the workers had been given the bones and stored them in a shoebox. Guarducci reported that to Pope Paul VI, who in 1968 declared that the remains were "identified in a way that we can consider convincing."

Paul's statement was the closest thing to a statement of authenticity the bones ever received from the Vatican, though Francis' Nov. 24 presentation of the bones at a Mass is probably a close second.

The reliquary was returned to its bronze display case beneath St. Peter's Basilica's main altar after the Mass, where they can be viewed only on a specially arranged tour.

Outside the Vatican, the jury is still out about their authenticity, with experts weighing in on both sides of the debate.

"It's very difficult for me to believe the bones are authentic," said Antonio Lombatti, a church historian. "It's one thing to say the bones are 2,000 years old and that they have the characteristics we believe to be those of St. Peter. But recall that in the time of St. Peter, Christianity was illegal. Things were hidden and moved around hastily.

"A man of faith, of course, may see things differently, but the truth is that from a factual perspective there is no way to know if something that old is real or not," Lombatti said.

But Lorenzo Bianchi, a leading archaeologist and expert on church relics, disagreed.

"Every case is different and must be measured by its merits," he said. "There are many ways to verify and I suppose there is no way to be 100 percent sure, but from circumstances and records we can say some specific things about these bones: that they were buried there some time (before the period) between 114 and 120 A.D., that Constantine believed them to be authentic, that other records seem to support that. I think we can be as certain as we can reasonably expect to be about this."

Officially, the Vatican remains mum on the subject of the authenticity of the bones, referring to Paul VI's 1968 statement. And the faithful on hand for the Nov. 24 Mass -- marking the end of the Vatican's Year of Faith -- were mixed in their reaction, with several amazed to be in the presence of such a relic and others expressing doubts.

Peter Manseau, a Maryland author whose 2009 "Rag and Bone" explored the global devotion to holy relics, said it might not matter if the bones were real or not.

"I think that in the end, the authenticity may be beyond the point," Manseau said. "Their relevance doesn't really depend on their being what they say they are. They are more important as symbols of faith rather than as some kind of forensic evidence."

KRE/AMB END LYMAN