Much like how the gods would move with Western Civilization, so to did the spirit of the Oracle. Human maidens who had the gift of clear sight could inherit the power and pass it on to another when the time came. This continued until the death of Maria di Angelo, a lover of Hades, right before the start of World War II. The Oracle had given the first Great Prophecy, claiming that a child of Zeus, Poseidon, or Hades would have to make a choice that would preserve or raze. Not wanting to take any chances, Zeus ordered that Hades two children, Bianca and Nico di Angelo, be sent to Camp Half-Blood to be trained. Hades however was mistrusting of his brother and asked Maria to follow him into the Underworld where he could protect them and that there wasn't much time as Zeus' deadline had already passed a week ago. Maria didn't believe the gods would be so cruel as to kill them and went upstairs to grab her purse. At that moment, Zeus sent down a bolt of lightning to kill the children. Hades managed to protect the children, but was not able to save Maria and cursed Zeus in his anger.
After Hades' children and Maria's body were taken away by the furies, the current Oracle appeared before Hades. While Hades blames the girl for the death of his wife and threatens to destroy her, she counters saying the power of Delphi protects her and that she had warned him to hide the children sooner. Hades still blames her as this all came about because of her prophecy. The Oracle remains unflinching until Hades claims that even if he can't kill her, he can curse her. Hades then claims that as long as his children remain outcasts and he is forced to labor under her Great Prophecy, the spirit of the Oracle would never pass on to another host. Even after death, the spirit would never move on and would continue to speak prophecies until her body withered away to nothing but dust.
While the Oracle could no longer change bodies, after her death the only person to know this was Hades. Eventually, May Castellan attempted to take on the spirit of the Oracle of Delphi after she had been dead for over twenty years. While Chiron encouraged her, Hermes (her lover) protested against it as it seemed humanity had lost the power to hold the spirit. May however wanted to host the Oracle and pushed for it knowing the risks. The process didn't take however and May was cursed with horrible visions of the future about her son and small occasions where she would talk about his fate in a crazed manner. The body of the Oracle continued to remain in the attic and no one else was allowed to try and take on the spirit until Rachel Elizabeth Dare.