Editor's note (Mon 8 April 2024): This study has been retracted over concerns as to how radiocarbon dating was used in the research. A full explanation of the retraction is available here. Our original story appears below:

A giant underground pyramid-like structure hidden beneath a hillside in Indonesia far outdates Stonehenge or the Giza Pyramids and, according to a new paper, may come to rival the oldest megalithic structures ever built by human hands.

Remember the name Gunung Padang.

The exceptional hillside of ancient stone structures on the island of West Java is sacred to locals, who call this kind of structure a 'punden berundak', meaning stepped pyramid, for the terraces that lead to its peak.

Archaeologists have barely brushed the surface of the site, and yet it is already considered by many researchers to be a "remarkable testament" to human ingenuity.

Gunung Padang is, potentially, the oldest pyramidal structure in the world, built atop an extinct volcano before the dawn of agriculture or civilization as we know it.

It's worth flagging that there is controversy over whether the site involves human-made structures or a pyramid at all, or whether many of the features here are a result of natural forces.

But an extensive analysis of Gunung Padang, which means 'mountain of enlightenment' in the local language, suggests that an ancient civilization "meticulously sculpted" the natural hill of lava into the core of a pyramid-like structure long ago.

According to new data from scientists in Indonesia, its interior could also very well be hiding large open chambers filled with unknowns.

Top Gunung Padang
Gunung Padang. (Ade lukmanul Hakim/Getty Images)

According to the new paper, the first radiocarbon dating of the site indicates that initial construction may have began sometime in the last glacial period, more than 16,000 years before the present and possibly as far back as 27,000 years ago.

To put that in perspective, Göbekli Tepe, which is a massive stone assembly in present-day Turkey, is currently considered to be the oldest known megalith in the world. It dates to 11,000 years ago.

Surface Gunung Padang
The megalithic stones seen on the surface of Gunung Padang. (Natawidjaja et al., Archaeological Prospection, 2023)

The results of the current study on Gunung Padang come after many years of careful analysis.

Between 2011 and 2015, a team of archaeologists, geologists, and geophysicists, led by geologist Danny Hilman Natawidjaja at Indonesia's National Research and Innovation Agency, used a variety of techniques, such as core drilling, ground penetrating radars, and subsurface imaging, to probe the cultural heritage site.

Natawidjaja and colleagues suggest that Gunung Padang was built in complex and sophisticated stages, the deepest part of which lies 30 meters down.

Gunung Padang Map
Simple reconstruction of Gunung Padang with all four units and their various burial levels. (Natawidjaja et al., Archaeological Prospection, 2023)

The researchers think that this core part of the structure was probably built between 25,000 and 14,000 BCE, but was then abandoned for several millennia.

According to the paper, construction started again around 7900 to 6100 BCE, expanding the core mound of the pyramid with various rocks and gravelly soils, with some further building work taking place between 6000 and 5500 BCE. Intriguingly, the team suggest that at this point, the builders seem to have purposefully buried or built over some older parts of the site.

The final architects of the pyramid arrived around 2000 to 1100 BCE, the researchers say, adding top soil as well as stone terraces characteristic of a punden berundak. This is the part that's mostly visible today.

Gunung Padang Stones
The surface stones of Gunang Padang. (Ali Trisno Pranoto/Getty Images)

"The builders of Unit 3 and Unit 2 at Gunung Padang must have possessed remarkable masonry capabilities, which do not align with the traditional hunter-gatherer cultures," write the team of researchers.

"Given the long and continuous occupation of Gunung Padang, it is reasonable to speculate that this site held significant importance, attracting ancient people to repeatedly occupy and modify it."

Further excavations are needed to understand who these prehistoric people were and why they built the things they did.

When researchers probed the interior of the hillside using seismic waves, they found evidence of hidden cavities and chambers, some up to 15 meters long with ceilings 10 meters high. It's unclear whether these were constructed by humans.

The team now hopes to drill down into these areas. If they do encounter any chambers, they plan on dropping a camera down into the darkness to see what lurks below.

"This study exemplifies how a comprehensive approach integrating archaeological, geological and geophysical methods can uncover hidden and vast ancient structures," the team concludes.

While controversy remains, this undoubtedly won't be the last you hear of Gunung Padang.

The study was published in Archaeological Prospection.

Editor's note (8 November 2023): This article has been updated to flag the controversy surrounding Gunung Padang and highlight that it could also be a natural site that hasn't been constructed by humans.