The artifact was a part of the Olympos Project and was capable of transmutating its host. The Isu scientists Aita and Juno used this artifact to create the Hekatonchires, a new weapon meant to "strike fear so deeply into the hearts of humanity, they would never consider revolt" and force Poseidon to name Aita as the new Dikastes Basileus.
The Spartan misthios Kassandra fought and defeated the creature in combat, before approaching the artifact at the creature's chest, taking it out and containing it. The Hekatonchires disintegrated, leaving a number of human remains behind. Later, she used it in conjunction with the Staff of Hermes Trismegistus and the Prize of Cerberos to activate a mechanism that initiated the destruction of Atlantis.
Behind the scenes
Due to the Hekatonchires' nature as a simulation, it is unknown whether it or a similar creature was ever a part of the Olympos Project proper and if the Prize of the Hekatonchires was an actual Atlantis artifact outside the simulations, though the Essential Guide considers as Atlantis artifacts only the four items used as keys for the city.