The world's oldest pyramid, or are they dreaming?

It has been raining at Gunung Padang, and the grass on the mountain's precipitous eastern slope is slick with water and mud. Geologist Danny Hilman, though, is undeterred. While others slip and fall around him, he trudges expertly down this hill tucked away among the volcanoes 120 kilometres south of Jakarta to show off the two big holes he's dug.

Since Dutch colonists found it in 1914, Gunung Padang has been known (though not particularly widely) as the largest of a number of ancient megalithic sites in Indonesia. Here our prehistoric forebears, moved by the strikingly shaped columns of volcanic rock in the area, built terraces into the mountaintop and arranged and stacked the stones for whatever indiscernible purpose motivated them.

Hilman, though, thinks that, under the surface, there is more to it. Much more. If he's right - and Indonesian president Susilo Bambang Yudhoyono is enthusiastically encouraging his investigations - then buried beneath the piles of ancient stone is by far the oldest pyramid on the planet. It could, according to Hilman, predate the next oldest by a dozen millenniums or more, suggesting an advanced ancient civilisation in Java perhaps even older than the appearance of agriculture.

"It's older than 9000 [years] and could be up to 20,000 [years]," Hilman says, as he sits on a fallen column of stone. "It's crazy, but it's data."

Hilman, a senior geologist at Indonesia's Geotechnology Centre, believes that most of this 100-metre tall hill is actually man-made, built up in three stages over the centuries by three different cultures. If he is right, the find would rewrite global prehistory in the same way as the discovery of a mini-human "hobbit" on the eastern Indonesian island of Flores rewrote palaeoanthropology.

The idea is being pushed by Hilman and a man called Andy Arif, a former activist turned politician, and member of Yudhoyono's Democratic Party.

In May, Hilman, who holds a PhD from the California Institute of Technology, was summoned to brief Yudhoyono on his findings. So impressed was the president that he appointed a government taskforce to investigate further, while Andy and Hilman continued with their work. The President urged haste, describing the team's work as a "task of history ... of important value for humanity". Yudhoyono even offered the services of the national army's heavy earth-moving equipment.

The proving of ancient ruins among the banana palms and tea plantations of Cianjur has since taken on the aura of a nationalistic quest.

Today's test involves one in a series of geo-electric surveys. Men in gumboots array long loops of yellow cable on huge columnar rocks denuded of their topsoil.

Hilman stands on the muddy edge and points out what he says are patterns in the arrangement of the rocks. These patterns, he says, reflect the geological testing already performed — that stones usually found upright have been laid horizontally on beds of gravel. Some are stuck together by an ancient form of glue, he says, which he has had carbon dated, yielding the dates he recites. Below this there are walls, he says, rooms, internal steps and terraces, all evidence of a massive building, of human intelligence and planning.

"The structure of the building is very good, it's been defined by many, many lines of the geo-electric surveys, even 3D, even GPR [Ground Penetrating Radar] ... and core samples," Hilman says.

"We conclude that the archaeological site, the arrangement of these columnar joints, has laminated the entire hill. And we also think it's not just one layer of building, of culture, but it's multiple layers. So we think that we have found archaeological human structures or features at least down to 15 metres depth."

"It's huge," he says. "People think the prehistoric age was primitive, but this monument proves that wrong."

These views, though, are much disputed. A petition signed in April by 34 Indonesian archaeologists and geologists and submitted to Yudhoyono, agrees that the upper part of Gunung Padang is "the largest megalithic structure in south-east Asia", but the experts are deeply suspicious of the Arif team's methods and motives, and the geological flag-waving it's trying to invoke.

The petitioners do not like Arif's "plans to involve common people as volunteers to support the "Red-and-White Glory Operation in Gunung Padang which they call research". Red and white refers to the colours of the Indonesian flag.

"This activity is carried out without scientific norms of conservation knowledge," the petition continues.

The petitioners believe the excavation threatens the preservation of the existing site, and hint strongly that archaeologists, as opposed to geologists, should be involved. One of them, vulcanologist Sutikno Bronto, says Gunung Padang is simply the neck of a nearby volcano, not an ancient pyramid.

"Danny Hilman is not a vulcanologist. I am," he tells Fairfax Media. As for the carbon-dated cement between the stones, on which Hilman relies for his claims about the age of the site, Sutikno believes it is simply the byproduct of a natural weathering process, "not man-made".

Other sceptics are even tougher. One, an archaeologist who does not want to be named since the President took such an interest, says the presidential taskforce is deluding itself.

"In the Pawon cave in Padalarang [about 45 kilometres from Gunung Padang], we found some human bones and tools made of bones about 9500 years ago, or about 7000 BCE. So, if at 7000 BCE our technology was only producing tools of bones, how can people from 20,000 BCE obtain the technology to build a pyramid?" the archaeologist asks.

"In archaeology we usually find the 'culture' first. Then, after we find out the artefact's age, we'll seek out historical references to any civilisation which existed around that period. Only then will we be able to explain the artefact historically. In this case, they 'found' something, carbon dated it, then it looks like they created a civilisation around the period to explain their finding."

If the ancient civilisation of Gunung Padang is, indeed, a credulist's dream, it would not be the first time the Indonesian President had been seduced by a beautiful illusion. In 2008, a confidence man promised to power Indonesia with "blue energy" — fuel made only from water. Yudhoyono allocated $1.2 million to the project and visited the centre three times before its proponent simply disappeared, fetching up later in hospital, his idea in tatters.

Hilman, though, is undeterred. He is certain in his research, though he knows he still has some persuasion to do. "It's a strong case but not an easy case. We are up against the world's belief."