The Ancient Oculus was an artifact recovered from the Bastion of Eraka no Kimbul by Facade. It contained incredible amounts of energy, allowing Facade to destroy the mercenary fleet that Rogni Bronzebeard had hired to transport his army to Hesperia. According to Facade, this depleted most of its energy stores.
Facade was lying. The Oculus in fact contained more energy than he could have fathomed, but the techniques used to lock it away were from an entirely different school of magical thought than the way he and the rest of Azeroth's mages operated. His very instinct fought against extraction of the magical energy within. At Jackie Ketkhin's suggestion, he recruited magical prodigy Lunarus to unlock the secrets of the Oculus.