The Ancient Forge, otherwise known as the Forge of Hephaistos, was an Isu vault located on the Greek island of Andros. The Ancient Forge was the site of the creation of a number of Precursor relics and Pieces of Eden, including the Spear of Leonidas.
The vault was discovered by the Greek historian Herodotos during his travels prior to 431 BCE. However, as it could only be opened by Isu relics, Herodotos was unable to enter the vault and learn its secrets. The Chimera, a member of the Silver Vein branch of the Cult of Kosmos, also discovered the location of the vault, demanding men and resources to aid her expedition to the vault.
After meeting the Spartan misthios Kassandra, Herodotos accompanied the misthios to the island. Kassandra sought out the entrance, finding remains of people who had attempted to enter the structure. She used her heirloom, the Spear of Leonidas, to open the vault. Once inside, Kassandra used one of the molds to upgrade her spear with the Artifact Fragment she had collected from the Cult of Kosmos.
- The Ancient Forge contains at least four unique molds; one for the Spear of Leonidas, one for the Sword of Damokles (as speculated by Kassandra), and two more for what appear to be the Minotaur's axe and Polyphemos Cyclops Bludgeon.
- As demonstrated with the Spear of Leonidas, even if the weapon is broken, the Forge will still upgrade and improve it to the point of repairing it (as the broken portion of the spear gradually turned into a pommel with each upgrade).
- No matter how often the Spear is upgraded, it will always appear in its default broken state in cutscenes.