Detective work by a British historian has unearthed information that could enable thousands to piece together their family histories.
Peter Barton was commissioned to carry out research into the identities of World War I casualties discovered in a mass grave at Fromelles in France.
He was given access to the basement of the Red Cross headquarters in Geneva.
There, he was allowed to examine records that have lain virtually untouched since 1918.
He estimates that there could be 20 million sets of details, carefully entered on card indexes, or written into ledgers.
They deal with the capture, death, or burial of servicemen from over 30 nations drawn into the conflict; personal effects, home addresses and grave sites cover page after page.
All were passed to the Red Cross by the combatants; volunteers logging the information by hand before sending it on to the soldiers' home countries.
"To a military historian, this was like finding Tutankhamen's tomb and the terracotta warriors on the same day," he told me.
"I still can't understand why no-one has ever realised the significance of this archive - but the Red Cross tell me I'm the first researcher who has asked to see it."
The records could potentially reveal the whereabouts of individuals whose remains were never found, or never identified. Grave after grave in the World War I cemeteries mark the last resting place of an unknown soldier.
But that presents the Red Cross with an unprecedented challenge; the paper records must now be conserved, and digitised. More than £2m has already been set aside for a project that will begin this autumn, and which is likely to involve experts from all over Europe.
The Red Cross hope to have the archive online by 2014, 100 years after the start of World War I. They believe that the care and patience of their volunteers during the conflict coupled with today's technology will provide a key to unlock the past.
But this site is also home to one of the word's most remarkable historic archives; personal details which have lain virtually untouched for decades.
Their significance only came to light after Peter Barton had been commissioned by the Australian government to carry out research, following the discovery of a mass grave on World War I battlefield at Fromelles in France.
That trail led him to the Red Cross Museum in Geneva, and to the card indexes and registers compiled between 1914 and 1918; during that period the Red Cross had acted as a go-between, logging, and passing on information to 30 countries drawn into the conflict.
Those details included whereabouts of prisoners, their condition or injuries at the time of capture, and the location of field burials.
Details which no longer exist in the UK, but here, in dusty cardboard boxes Peter Barton found the original indexes; thousands upon thousands of cards; dozens of registers.
Some of the records refer to other mass graves, with exact directions as to where they were dug, and the identities of the soldiers who were buried. Where possible, the registers include home addresses and next of kin.
In the World War I cemeteries, headstone after headstone marks the last resting place of an unknown soldier.
The names of the missing line the walls of memorials across France and Belgium, and until now, the trails followed by new generations ended with family histories still incomplete.
The organisation's head of press, Florian Westphal, admitted they had never faced a challenge quite like this: "First we have to make sure that we preserve the original records," he told me.
"Then, this autumn, we will begin the process of digitising the World War I section of the archive - we expect that phase of the project to cost around four million Swiss Francs."
The Red Cross say they'll need expert help from other countries, and will almost certainly ask for volunteers to join their own archivists. They aim to have the archive available on the web by 2014, a century after World War I began.
But that's only the start; the careful record-keeping extended through World War II, and on to more recent conflicts.
I was shown the rows of metal shelves which contain millions more personal stories; more index cards neatly packed into boxes. Public access here would require significantly more effort, and more cash which is simply not available at this stage.
Back in the World War I archive, Peter Barton was leafing through page after page of handwritten names - all men who had died on the first day of the Battle of the Somme - lives ended far from home, but, thanks to the patience and care of Red Cross staff all those years ago, their stories may soon be told.