Archaeologists have found ancient human stone tools dating to more than 1 million years ago on the Indonesian island of Sulawesi. The tools are 5 times older than the previous earliest evidence of humans on the island.

While the identity of the stone tool makers remains a mystery, the archaeologists believe the discovery could help explain the spread of early humans through Southeast Asia and may even shed light on the origin of the “hobbits” of nearby island Flores.

Map of Southeast Asia showing the location of Calio in southern Sulawesi. Credit: B. Hakim et al., Nauture (2025).

The new Sulawesi stone tools were found at the Early Pleistocene site of Calio.

During this ice age period, water was locked in massive ice sheets at the poles and sea levels around the world may have been up to 100m lower than today. Nonetheless, Sulawesi was separated from the rest of the Indonesian archipelago and Southeast Asia by a deep sea.

The discovery of the Calio stone tools, therefore, suggests that early hominins made a major deep-sea crossing to Sulawesi much earlier than previously thought.

Stone tools excavated from Calio, Sulawesi. Credit: M.W. Moore/University of New England.

A total of 7 stone artefacts were uncovered from the sedimentary layers of a sandstone outcrop at Calio. Today, the site is a corn field in the island’s south. Palaeomagnetic dating of the sediment and direct dating of a pig bone in the same layer show the artefacts are at least 1.04 million years old and possibly up to 1.48 million years old.

The findings are presented in a paper published today in Nature.

Indonesia’s islands represent a unique part of the human story. Ancient land bridges between the more than 17,000 we see today allowed early hominins and early modern humans to make the trek from mainland Asia to the Pacific, including Australia.

Just 500km south of Calio on the island of Flores is one of the most enigmatic and imagination-stirring ancient humans, Homo floresiensis – also known as “hobbits”.

Homo floresiensis fossils and stone tools date to about 200,000 to 50,000 years ago. This ancient human species grew to barely 1m tall, leading archaeologists to theorise that it is a descendant of Homo erectus which evolved to be small through a process called island dwarfism.

The team behind the Calio discovery has found other ancient hominin sites around region including stone tools from 1.02 million years ago on Flores and nearly 200,000 years ago on Sulawesi.

The island of Luzon in the Philippines has hominin evidence from 700,000 years ago.

“This discovery adds to our understanding of the movement of extinct humans across the Wallace Line, a transitional zone beyond which unique and often quite peculiar animal species evolved in isolation,” says senior author Adam Brumm, a professor at the Australian Research Centre for Human Evolution at Queensland’s Griffith University.

“It’s a significant piece of the puzzle, but the Calio site has yet to yield any hominin fossils; so while we now know there were tool-makers on Sulawesi a million years ago, their identity remains a mystery.”

“Sulawesi is a wild card – it’s like a mini-continent in itself,” Brumm adds. “If hominins were cut off on this huge and ecologically rich island for a million years, would they have undergone the same evolutionary changes as the Flores hobbits? Or would something totally different have happened?”

A million years ago Sulawesi was probably made of a series of smaller islands with rich and diverse habitats.

“The environment in the vicinity of Calio would have consisted of a braided river channel on a coastal plain,” Brumm says in an email to Cosmos.

He wonders what the find could mean for archaeology in the region.

Excavations at Calio in southern Sulawesi, Indonesia. Credit: BRIN.

“Some scholars have suggested that the early hominins of Flores actually originated from the island of Sulawesi, so the discovery that the hominin presence on Sulawesi is at least as old as that on Flores, if not older, certainly opens the door to this possibility.”

Brumm also points to the fact that there remain unknowns about the Calio artefacts – who made them and what were they used for?

“We don’t know the function of the stone tools, but they are sharp-edged flakes of stone that no doubt would have been useful as general-purpose cutting and scraping implements,” Brumm says.

Future investigations could uncover more clues.

“Very little of this huge island (world’s 11th largest) has been systematically investigated by archaeologists – I strongly suspect there are some exciting discoveries in store for researchers who are persistent, and lucky, enough.”