Photos discovered in a Roman library show trade relationship between Australia and Indonesia

The images, taken in Makasar, Indonesia in the 1870s, show Indigenous men and children from Australia's north. Researchers believe the group moved with visiting Asian fishing crews during the 1700 and 1800s.

Aboriginal elders say the images depict Yolngu people, from Arnhem land. The photos match with oral history of ancestors moving away. It is this knowledge that is helping researchers piece together the intricate puzzle.

It is unknown if they left Australia voluntarily. Some people seem to have returned home, though dates are unclear.

ACM spoke with a key researcher in the field to find out more about this story.

We may not have all the information yet, but the images prove something vital. Migration and trade from Australia happened prior to European settlement.

Monash University professor Lynette Russell researches connections between Australian Indigenous people and other continents prior to the British arrival in 1770. She has been working on this project for three years.

She said it was crucial for research to demonstrate Aboriginal people "were not some isolated group stuck out in the middle of the south pacific ocean".

"They were, in many ways, connected to international events such as the trade and spice routes," she said.

Professor Russell believes Indonesians come to collect sea cucumbers - known as trepang - which were boiled, dried out, and traded in China as a medicinal.

The voyages took around six months and involved skilled fisherman who would collect the trepang. Some accounts suggest Makassarese exchanged the cucumbers for things like cloth, knives and rice.

"[It was] part of the constant trade between Indochina, Indonesia and of course China itself, and various other parts of south east Asia, where people were trading," Professor Russell said.

Professor Russell is unsure how many Aboriginal people joined the Makassarese on their homeward trip but said numbers do not change how crucial the history is.

"These were really formative experiences. Although there weren't necessarily vast numbers of people, I think the actual experience was really quite important," she said. "These people would have come back to tell community lots of stories."

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"There are plenty of oral traditions - there's songs," she said. "The people of Makasar also have stories of their grandparents and great-grandparents heading off on the monsoon winds."

The team has examined things like linguistic terms and inclusion of Indonesian words into Indigenous languages, migration routes and connection with Indigenous communities in 'Marege' - northern Australia.

Researchers are now searching for descendants worldwide, with DNA testing a possibility. They hope to find out more about the scale of migration from northern Australia to Indonesia.

Professor Russell will visit Makasar for a second time later this year, where she will work with locals and researchers to discover more detail about the trades.