Passage 5.16.8
ὁπόσα δὲ ἢ ταῖς ἑκκαίδεκα γυναιξὶν ἢ τοῖς ἑλλανοδικοῦσιν Ἠλείων δρᾶν καθέστηκεν, οὐ πρότερον δρῶσι πρὶν ἢ χοίρῳ τε ἐπιτηδείῳ πρὸς καθαρμὸν καὶ ὕδατι ἀποκαθήρωνται. γίνεται δέ σφισιν ἐπὶ κρήνῃ Πιέρᾳ τὰ καθάρσια· ἐκ δὲ Ὀλυμπίας τὴν πεδιάδα ἐς Ἦλιν ἐρχομένῳ πρὸς τὴν πηγὴν ἀφικέσθαι τὴν Πιέραν ἔστι.
All those duties appointed either to the sixteen women or to the Eleian judges are not performed before they purify themselves with a suitable pig used for cleansing rites and water. Their purification ceremonies take place at the Pierian spring, which is encountered by one who travels from Olympia across the plain toward Elis.