The Treaty of Elysia was an event in Elysian history. It took place fifteen years prior to the events of Metroid Prime 3: Corruption. When the Galactic Federation entered SkyTown, the Elysians were awoken from a 1435-year slumber to defend the fortress, assuming the Federation were enemies. However, they were proven otherwise. The treaty was signed, stating that the Federation would supply the Elysians with supplies, fuel and parts in return for letting them use SkyTown as they saw fit. Aurora Unit 217 was installed into SkyTown, allowing the Elysians to assist the Federation in acquiring new research that would prevent disasters throughout the galaxy.