The Antikythera Mask
The artifact is a white mask styled similarly to Greek relics depicting the deity Hermes. It was intially recovered from a site close to that of the Antikythera Mechanism . The mechanism and the mask were retrieved and replaced with fakes by Sinon and Jones squad operating under the auspices of Project: Nightfall.
The two items work in concert to form a kind of Soul Stone/Masque repository. Once the proper alignment on the machine is found, memories and parts of one’s soul can be stored or swapped with those left by prior users.
Despite its age and the recency of the find, the artifact apparently contains the souls and memories of mages from throughout history. How this has happened is not currently known.