PORTUNALIA. – A festival celebrated on August 17 in the most ancient Roman calendar, dedicated to the god Portunus, whose character is only vaguely and uncertainly described in literary sources (god of doors or of harbors). The ancient importance of the god is evident from the fact that he had his own flamen, called Portunalis, though the only known duty of this priest was to anoint, on certain occasions, the sacred arms of the god Quirinus.
The Portunalia were celebrated on the banks of the Tiber, near the Pons Aemilius, where the temple of the god stood; in a later calendar the day is designated, not as P., but as Tiberinalia. This connection with the river or with waters seems to be reflected in the mythological identification of Portunus with the Greek Melicertes-Palaemon. On the other hand, Portunus is inseparable from the sphere of Janus: the Portunalia are the day of dedication of an ancient temple of Janus; and a rite of the Portunalia consisted in burning keys, while the key is known as an attribute of Janus.