There has long been speculation about underground chambers beneath the monument known as the Khaznah, or Treasury, in the ancient city of Petra, Jordan – and now it has been confirmed.

Archaeologists recently discovered a tomb containing at least twelve human skeletons and artifacts, estimated to be at least 2,000 years old, CNN reported.

The elaborate monument, carved into pink sandstone cliffs, has been featured in several films. It is best known as the location of the Holy Grail in the 1989 film ‘Indiana Jones and the Last Crusade’.

In 2003, two graves were found under the left side of the monument during an expedition led by Dr. Pearce Paul Creasman and other archaeologists, leading to theories that they were not alone.

Creasman, executive director of the American Center of Research, and his team used a remote sensing technique called ground-penetrating radar, which uses pulses to detect underground objects to see if the physical features on the left side, where the first two graves were found, matched with the features on the right.

They found strong similarities between the two sides, giving them the evidence they needed to get permission from the government in Jordan to start digging.

“I think we have something,” Creasman told Josh Gates, host of Discovery Channel’s “Expedition Unknown,” according to CNN.

They and a film crew excavated the newly uncovered grave in August, but the most shocking discovery was what was inside.

Most of the tombs discovered in the ancient city are empty or disturbed, but this one was filled with complete skeletal remains and grave goods made of bronze, iron and ceramic.

Researchers say the find may be the largest collection of human remains found in one spot in Petra.

The pair of graves uncovered 20 years ago by archaeologists from the Jordan Department of Antiquities contained partial skeletal remains, although it is unclear how many were found because the data has not been published, Creasman said.

“This is an extremely rare discovery; In the two centuries that Petra has been explored by archaeologists, nothing like it has ever been found before,” Gates said. “Even for one of the most famous buildings in the world… there are still enormous discoveries to be made.”

Among the well-preserved excavated artifacts were several vessels – and one skeleton was found holding a ceramic chalice that resembled the mythical Holy Grail from which Jesus drank at the Last Supper.

“It was really this great moment in history that imitated art,” Gates said.

Although the human remains were intact, they were more fragile than expected — some discovered with mold — possibly due to humidity and seasonal flooding, as well as the porous sandstone surrounding the grave that retained moisture, Creasman said.

Because the burial was intact, it gave archaeologists a rare insight into the Nabataeans, ancient Arab nomads whose desert kingdom flourished from the 4th century BC to 106 AD, Creasman explained.

“We were hoping to find something that could tell us more about the ancient people and the place – human remains can be a very valuable tool in that regard,” Creasman said. “The burials in this grave are articulated, so the bones have not been jumbled around and moved, so that is extremely rare.”

“They must be hugely important people because where they are buried is such prime real estate; it really is the main entrance to the city,” Gates added. “I think learning who they are will really help unlock part of the Treasury Department story.”