Scientists have discovered that there is a "very real risk" that the holiest site in Christianity may collapse if nothing is done to shore up its unstable foundations.

A scientific team from the National Technical University of Athens (NTUA), which has just completed the restoration of what is traditionally believed to be the tomb of Christ in Jerusalem, warns that additional work is needed to prevent the shrine and surrounding complex from experiencing significant structural failure.

"When it fails, the failure will not be a slow process, but catastrophic," says Antonia Moropoulou, NTUA's chief scientific supervisor.

View Images During restoration work, scientists discovered that much of the Edicule rests on a foundation of unstable rubble, decayed mortar and tunnels. Photograph by Oded Balilty, AP for National Geographic

The Edicule (from the Latin aedicule, or "little house"), a small structure within the Church of the Holy Sepulchre, encloses the remains of a cave that has been venerated since at least the fourth century A.D. as the tomb of Jesus Christ.

Restoration of the Edicule reveals that much of the 19th-century shrine and its surrounding rotunda, which host millions of annual visitors, appear to be built largely on an unstable foundation of crumbled remnants of earlier structures and is honeycombed with extensive tunnels and channels.

EXCLUSIVE: A Closer Look Inside Christ's Unsealed Tomb

View Images A conservator cleans the surface of the stone slab venerated as the final resting place of Jesus Christ. Photograph by Oded Balilty, AP for National Geographic

While the year-long restoration of the Edicule is being celebrated today in Jerusalem with a ceremony at the church, scientists and church leaders are grappling with the new evidence for significant risks that the engineering work has revealed.

Layers of History Pose Risk to Future

The most recent NTUA report provided to National Geographic reveals that much of the risk posed to the tomb is due to the rich history of the venerated site.

Archaeologists believe that some 2,000 years ago, the site was the location of a defunct limestone quarry that eventually housed tombs of the Jewish upper class. At least half a dozen such tombs have been identified within the grounds of the church, in addition to the tomb traditionally believed to be the burial place of Jesus.

A Roman temple built on the site in the second century was razed by Constantine, the first Christian emperor of Rome, around 324 A.D. to reveal what was believed to be the tomb of Christ.

The shrine built by Constantine around the tomb was partly destroyed by Persian invaders in the seventh century A.D. and destroyed again by the Fatimids in 1009. The church was rebuilt in the mid-11th century. The Edicule was later altered by the Crusaders and restored again in the 16th and early 19th centuries. Its current form encloses several earlier construction phases.

The domed rotunda that surrounds the Edicule is believed to mark the footprint of the original Constantinian church, and possibly the Roman temple that preceded it.

Tunnels Beneath the Tomb of Christ

The recent survey beneath the floor of the Edicule and rotunda, conducted during the restoration project, confirmed some of what scientists have long suspected while revealing previously unknown risks to the stability of the entire 3,000-square-foot survey area.

View Images The rotunda that surrounds the Edicule is believed to mark the footprint of the first church on the site, built around 325 A.D. Photograph by Oded Balilty, AP for National Geographic

Ground-penetrating radar, robotic cameras, and other tools show that some portions of the Edicule's foundation sit on the rubble of earlier buildings. Other parts rest directly on the brink of very steeply sloped, quarried bedrock. Foundation mortar has crumbled due to decades of exposure to moisture from drainage channels that run several feet beneath the rotunda floor.

Other unexplained tunnels and voids run directly underneath and around the Edicule. An eight-foot-deep archaeological trench dug south of the shrine in the 1960s sits beneath an unsupported concrete slab in an area where visitors have lined up to enter the tomb.

Several of the 22-ton pillars that hold up the dome of the rotunda rest on more than four feet of unconsolidated rubble.

The Successful Restoration of the 'Little House'

The structural integrity of the Edicule has been a concern for nearly a century, but disagreements among the different Christian sects that claim custody of the church, as well as a lack of financial resources, long hindered its repair.

Following a brief closure of the Edicule by Israeli authorities in 2015 due to safety concerns, the three major Christian groups that maintain primary control over the site—the Greek Orthodox and Armenian Patriarchates of Jerusalem and the Franciscan Custos of the Holy Land—signed an agreement in March 2016 to restore the shrine and the tomb it encloses.

View Images Christians pray inside the tomb of Jesus at the Church of the Holy Sepulchre. Photograph by Oded Balilty, AP for National Geographic

The Greek NTUA team charged with conserving the Edicule was also responsible for recent restorations of the Acropolis and Hagia Sophia.

The scientific team worked to reinforce the bowing walls of the Edicule, re-anchoring columns with titanium rods and re-grouting layers of masonry that go back more than a thousand years.

A ventilation system was installed, in part to alleviate the destructive soot from thousands of candles, and unsightly exterior girders erected by British authorities in 1947 were cut away with a plasma saw. The tomb itself was opened for the first time in centuries.

The work on the Edicule was successfully completed at a cost of nearly 3.5 million euros.

No Restoration Without Archaeological Excavation?

To address the risk of structural collapse at Christianity's holiest site, the NTUA now proposes a 10-month, six-million-euro project that will involve removing the fractured stone paving surrounding the Edicule, grouting foundation rubble and degraded mortar, and excavating more than 1,000 square feet of floor to install new sewage and rainwater drainage around the perimeter of the rotunda.

The work would be planned in a way to ensure minimal interruption to the approximately four million visitors who come to the tomb each year.

The possibility that the area below and around the tomb of Christ will be exposed raises new issues about the potential for archaeology at a site that has been the focus of veneration for nearly 2,000 years.

View Images A Coptic monk dusts the entrance to a chapel on the back of the Edicule. Photograph by Oded Balilty, AP for National Geographic

"This is one of the most complex sites for archaeology at one of the holiest sites in the world," says Martin Biddle, who studied the history of the Edicule for nearly a decade and published a seminal work on the subject in 1999.

There are "four or five major archaeological stages" under the Edicule, says Biddle, and any exposure of historical levels beneath the modern floor would warrant additional scientific investigation.

Restoration without archaeological excavation, Biddle says, "would be an intellectual scandal, and I choose my words very carefully."

The latest report will be shared with the three Christian groups following today's ceremony and a new agreement must be reached before any additional work can go ahead. Meanwhile, the NTUA team is processing the data it has collected and plans to make it available to other scientists on a future "Holy Sephulchre Information Platform."

"This work is a collective work," says NTUA's chief scientific supervisor Moropoulou. "It doesn’t belong to us, it belongs to all humanity."