I do not own PJO or HoO! Rick Riordan does!!
In book five of the series, The Last Olympian, the Great Prophecy is revealed:
A Half-Blood of the eldest gods,
Shall reach sixteen against all odds
And see the world in endless sleep
The hero's soul, cursed blade shall reap
A single choice shall end his days
Olympus to preserve or raze
The meaning:
1. Percy was a half-blood child of Poseidon, one of the eldest gods, otherwise known as the Big Three.
2. Percy reaches sixteen despite all of the numerous times he was almost killed by Luke/Kronos and his monsters.
3. Percy finds the whole city of Manhattan asleep from Olympus, so the war can go on without any of the humans interfering.
4. Percy handed Luke Annabeth's knife, the same knife that he gave her when she was little. He promised that they would be there for her and that they (including Thalia) would be a family.
5. Percy had to choose between giving Annabeth's knife to Luke and allow him to destroy himself or trying to destroy Luke himself.
6. Percy's choice would result in the destruction of Olympus, or preserving Olympus the way it is.
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Percy Jackson and Heroes of Olympus Prophecies
FanfictionI own nothing. The prophecies from PJO and HOO