The Battle of Half-Blood Hill was the conclusion of the Second Giant War and the final battle with Gaea and her army.
The Heroes of Olympus[]
The Blood of Olympus[]
Soon after the earth mother awakens, she partially traps three of the five cohorts in the monsters and use her powers to make the ground sink around their feet. The remaining cohorts and Greek forces head to help the trapped legionnaires and manage to break through the sea of monsters though but many more spawn under the command of Gaea. When the Argo II crashes into camp, the seven join the fight and successfully disconnect Gaea with the Earth with the help of Festus, who Leo managed to fix. She is then hit by a projectile launched by Octavian, with the auger attached to it, scattering her and killing Octavian and Leo Valdez, with the son of Hephaestus then being revived by the Physician's Cure. Meanwhile, the demigods manage to defeat Gaea's monsters, albeit with heavy losses.
After the battle, a mass funeral is held for the fallen Greeks and Romans. Both sides start to see one another as allies and form a quick friendship.