It has been described as the "worst 24 hours in Australia's entire history" - more than 5,500 of their troops were killed, wounded, or captured. The British, fighting alongside, lost 1,500.
War Historian Peter Barton has spent two years piecing together events on that day in 1916, in an effort to trace where the fallen were buried.
The dig at Fromelles has uncovered body fragments
German records indicated that they had been placed in a mass grave near the village of Fromelles, and aerial photographs seemed to bear this out.
Lambis Englezos, a retired art teacher from Melbourne, is in Fromelles' tiny museum. He's spent the past 30 years trying to convince his government to support the search for the missing Cobbers.
Now that day has arrived.
Half a mile away, screened from visitors, a team of archaeologists from Glasgow University are leading a team that also includes forensic scientists, recently arrived from Jersey, where they've been working on the child abuse enquiry at the former Haut De La Garenne children's home.
The Battle of Fromelles took place in north-east France
An Australian general, Mike O'Brien, is here to oversee the painstaking operation. He said the prime aim was to ensure dignity and respect for the fallen.
It was too early at this stage to predict what form of memorial would be appropriate.
At a media conference to announce the first remains had been found, archaeologist Tony Pollard said this was the largest investigation of its kind ever attempted.
His team believe there may be 400 British and Australian soldiers in the burial pits. It would be an emotional experience, even for those trained in such specialist work.
A short distance from the dig site lies the Australian Memorial Park, dominated by the cast figure of an Australian soldier carrying a wounded comrade.
A team of archaeologists are leading the dig
On the plinth beneath is the framed photo of another missing man - Pte Harry Willis, from Victoria.
His great-nephew, Tim Whitford, has travelled from Australia in the hopes that the mystery of Pte Willis' whereabouts may now have been solved.
During a survey last year archaeologists found a tiny medallion that may have been his.
Tim's view is simple - all those found should be given a full military funeral.
Whatever the cost, he said, nothing else would give the men the honour that they have been denied for so long.
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