Probatio

Propatoi is a position given to members of Camp Jupiter.

The Son of Neptune
Any newly arrived camper is given the rank of propatoi and a neck plate with the word on it. Propatoi are considered the lowest rank at camp as it is only given to people that haven't been claimed at Camp Jupiter or haven't accomplished some kind of amazing deed.

Frank was still this rank after a few months at camp when Percy arrived. He was charged with cleaning the armory and taking care of Hannibal the elephant, tasks considered beneath the other campers. Percy was also given this rank when Octavian accepted him into the Legion.

Later when deciding a cohort to place Percy in, Frank says that the Fifth Cohort, but because he is only a propatoi, he isn't allowed to represent Percy. Hazel who is a Centurion steps in and says she will represent Percy instead.

Frank didn't become a Centurion until Mars appeared and told him to lead a quest to Alaska. Because propatoi cant lead a quest, Reyna was forced to make Frank a Centurion. Percy also became a Centurion after helping to defend Camp Jupiter against the Giant Army, as Reyna removed his neck plate and congratulated him on become a praetor.