Because it was the custom at Athens to lead two pharmakoi … This cleansing served to ward off plagues of disease, and it took its beginning from Androgeus the Cretan [son of King Minos], because the Athenians were afflicted with a plague of disease when he died unjustly in Athens, and this custom began to be in force, to always cleanse the city with pharmakoi.
Pharmakos: Legendary Aitia ὅτι ἔθος ἦν ἐν Ἀθήναις φαρμακοὺς ἄγειν δύο … τὸ δὲ καθάρσιον τοῦτο λοιμικῶν νόσων ἀποτροπιασμὸς ἦν, λαβὸν τὴν ἀρχὴν ἀπὸ Ἀνδρόγεω τοῦ Κρητός, οὗ τεθνηκότος ἐν ταῖς Ἀθήναις παρανόμως τὴν λοιμικὴν ενόσησαν οἱ Ἀθηναῖοι νόσον, καὶ ἐκράτει τὸ ἔθος ἀεὶ καθαίρειν τὴν πόλιν τοῖς φαρμακοῖς.