An old swivel gun found on a remote Northern Territory beach in 2010 had been on the seabed for up to 250 years, dating tests show.
Scientists say this suggests previously unknown contact with Australian shores.
Darwin boy Christopher Doukas found the 107cm anti-personnel light artillery piece at Dundee Beach, south-west of Darwin, during an unusually low tide.
Geomorphologist Tim Stone says the find will help rewrite history through his Australian group Past Masters, a multidisciplinary team that explores historic mysteries.
"The cannon is one of the most significant historical artefacts ever found in northern Australia," he said.
The Past Masters believe Macassan or other sailors from Indonesia lost it about 1760 at the start of trepang trading as they explored in search of the ocean delicacy. An Indonesian vessel could have been blown off course to Australia.
Historians assumed Dutch explorer Willem Janszoon was the first European to reach Australia in 1606, just before fellow Dutch captain Dirk Hartog.
But the gun and other finds are intriguing, including five coins up to 1000 years old from the ancient African kingdom of Kilwa found in the Northern Territory in 1944.