Hagno

Hagno is one of the original nine nymphs from Greece that helped nurse the infant Zeus after attending Rhea in her labor. They hid Zeus in a cave from Kronos and he rewarded them with eternal honors.

The Mark of Athena
Hagno was trapped alongside eight other nymphs underneath the old Forum in Rome. She and her companions were invited into a nymphaeum by a son of Jupiter who promised that Rome would last forever. Abandoning their homes in Mount Lycaeus, the nymphs gave into temptation and moved into a nymphaeum where they lived for centuries. However, Rome was conquered, the aqueducts were diverted, and their master's home was destroyed. She and the nymphs couldn't leave because their life sources where bound to the place and their master didn't release them.

Centuries later, the nymphs were reduced to hideous savages and allied with Ephialtes and Otis who promised them they wouldn't suffer after they've killed Percy Jackson, Jason Grace, and Piper McLean. The three demigods enter the nymphaeum while searching for Nico di Angelo and are trapped by the nymphs. The nymphs dissolve into black oily water and try to extract the power of rain from Jason, an endless supply of water from Percy, and beauty from Piper by drinking.

Using the power of the cornucopia, Piper, Jason, and Percy sacrifice their power and their strength as if they were already dead in the form of clean water. The water is channeled out of the horn of plenty and manages to cleansed the nymphs. Returning to their beautiful selves, the nymphs leave to find new homes. Hagno tells them to follow the diverted aqueduct pipe line which leads into the hypogeum of the Colosseum where the giants reside. She then states that she can't wait to see Pan again to Percy's misery and vanishes.