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

As CNN reported, archaeologists recently discovered a grave containing at least 12 human skeletons and artifacts that are estimated to be at least 2,000 years old.

The ornate monument, carved into pink sandstone cliffs, has been featured in several films – most famously as the location of the Holy Grail in the 1989 film “Indiana Jones and the Last Crusade.”

In 2003, at a conference organized by Dr. Pearce Paul Creasman and other archaeologists-led expedition found two graves below the left side of the monument, leading to theories that they were not the only ones.

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 determine whether the physical features on the left, where the first two graves were found, were true match the functions on the right.

They found strong similarities between the two sides, giving them the evidence they needed to get permission from the Jordanian government to begin excavations.

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

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

Most tombs uncovered in the ancient city are either empty or destroyed, but this one was filled with complete skeletal remains and grave goods made of bronze, iron and ceramics.

Researchers said the find could be the largest collection of human remains found at one site in Petra.

The two tombs, discovered two decades ago by archaeologists from the Jordan Department of Antiquities, contained partial skeletal remains, although it is unclear how many were found because the dates have not been made public, Creasman said.

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

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

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

Although the human remains were intact, they were more fragile than expected – some covered in mold – possibly due to humidity and seasonal flooding, as well as the fact that the porous sandstone surrounding the grave traps moisture, Creasman said.

Since the burial was intact, the archaeologists had gained rare insight into the Nabataeans, ancient Arab nomads whose desert empire dates from the 4th century B.C. It flourished until 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 really valuable tool in that regard,” Creasman said. “The burials in this grave are articulated, so the bones have not been rummaged around and moved, so this is extremely rare.”

“They must be extremely important people because there is prime real estate where they are buried; It’s really the main entrance to the city,” Gates added. “I think finding out who they are will really help uncover some of the history of the Treasury Department.”