The Pontifex Maximus (Latin for "High Priest of the Gods"; literally meaning "Greatest Pontiff" ) is the highest position available in Camp Jupiter, used only during crisis situations. 
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Octavian, self-appointed Pontifex Maximus

In the Roman Republic, the Pontifex Maximus was the highest office in the state religion of ancient Rome and directed the College of Pontiffs. He had both political and religious authority.

Reyna Avila Ramírez-Arellano stated no demigod in Camp Jupiter's history ever elevated themselves to a rank of the pontifex; by doing so they would compare themselves to an emperor.

The Heroes of Olympus

The Blood of Olympus

While experiencing dream visions, Reyna sees Camp Jupiter's forces preparing for invasion on Camp Half-Blood. She then sees Octavian wearing a white cloth mantle which marked him as the pontifex.

After the underwater battle with Polybotes, Kymopoleia calls Jason Grace pontifex and reminds him to keep his promise about honoring every minor god there is with a shrine in Camp Jupiter and Camp Half-Blood.

After Gaea's defeat, Nico di Angelo mentions the Roman Senate thinks about electing Jason the new Pontifex Maximus.

Known Pontifices Maximi