Teams of experts are due to begin excavating the biggest Great War grave discovered in decades.
Up to 400 First World War soldiers from Britain and Australia are thought to lie in eight pits in the French countryside, where they were buried by German forces after battle.
Following a blessing, archaeologists will begin to recover the bodies on behalf of the soldiers' governments.
They will be supervised by the Commonwealth War Graves Commission (CWGC) which is building a new cemetery for the dead. The painstaking operation in Pheasant Wood, which lies near the village of Fromelles, around seven miles south of the French-Belgian border, is expected to take until the end of September.
The land was confirmed as a group burial site in May last year after a limited excavation revealed pits which had lain untouched since the Battle of Fromelles more than 90 years ago.
The hope is to use casualty records and DNA testing to assign identities to as many of the bodies as possible.
Roger Lee, historian for the Australian army, said: "We've never found sets of remains on this scale before. It's new ground for everybody."
The excavated remains will be taken to a nearby temporary mortuary and washed and dried in controlled conditions, before technicians work to calculate each individual's age, sex and size. Any artefacts found - such as kit parts or even a soldier's toothpaste - could help identification, allowing families to visit their fallen relatives' graves.
Next year the bodies will be permanently laid to rest in individual graves at the new CWGC cemetery nearby - the first war cemetery the commission has built in almost 50 years.
The Battle of Fromelles, which began on July 19 1916, was the first major battle on the Western Front which involved Australian troops. It proved disastrous for Allied forces - and records suggest that between July 19 and 21 the Australian dead at Fromelles amounted to 1,780, and the British loss 503.