For Portunus in Nova Roma see: Temple of Portunus (Nova Roma).
Father Portunus was an ancient Roman god, already on the archaic religion, to whom are granted the gates (porta), the harbours (portus), and more precisely the river harbour of Rome called portus Tiberinus, near the Forum Boarium where still today stands his temple.(See the picture on the right). His name also is written Portumnus. As the twelve other deities which each has his own flamen, Portunus is a local god of Rome and certainly a river god.
He shares some characteristics with Janus, the god of the house-doors ("janua"), while "porta" is rather gate, or town-doors. Both have as emblem the keys, offerred on August 17, during the celebrations of the god Portunus, the Portunalia, to bless the homes. Portunus also is depicted with an anchor.
Portunus also has to watch over the wheat stocking in the warehouses of Rome, perhaps invoked during the food retailing (annona), as supposes his representation on the Benevent Arch, where Portunus is hailed by the emperor Trajanus, which increased the Ostia harbour in size and took care in free wheat retailing to the beneficiary Roman citizens.
Portunus is Mater Matuta's son, the goddess which protects the Roman matrons and is honoured during the Matralia on june 11th, since Mater Matuta (Aurora) was assimilated to the Greek goddess Leucothea (The white goddess), former Ino, who were the mother of the marine deity Palaemon, assimilated to Portunus.
The antiquity of Portunus, his early character into the cults of the city and his originality are inferred from his name, his yearly festival and his flamen. His temple, near the Forum Boarium "Cattle market", where also were celebrated the Portunalia on August 17, and the portus Tiberinus is still standing.
You can see it near the Aemilius pons (ponte Rotto). The street to the port, called vicus Lucceius, went by the Porta Flumentana, in the Servian Wall, then passed between the Temple of Portunus and the Portus Tiberinus. This was the place of the processions and the ceremonies of the Portunalia, each August 17 (a.d. XVI Kal. Septembres).
The Portunalia are celebrated on a.d. XVI Kal. Sept. ‡ , the day when the temple of Portunus was consecrated. "Portunalia dicta a Portuno, cui eo die aedes in portu Tiberino facta et feriae institutae" (The Portunalia are named after Portunus, to whom on that day a temple in the Tiber port was made and consecrated.)  .
Poetry and literature
Leucothea Grais, Matuta vocabere nostris;
In Portus nato jus erit omne tuo:
Quem nos Portunum, sua lingua Palaemona dicet.
Ite, precor, nostris uterque locis!
For his epithet "Father", see Aeneid V,241:
- Et pater ipse manu magna Portunus euntem
Orphic Hymn 75 to Palaemon (trans. Taylor) (Greek hymns C3rd B.C. to 2nd A.D.) : "To Palaimon, Fumigation from Manna. O nursed with Dionysos, doomed to keep thy dwelling in the widely spreading deep; with joyful aspect to my prayer incline, propitious come, and bless the rites divine; thy mystics through the earth and sea attend, and from old sea’s stormy waves defend: for ships their safety ever owe to thee, who wanderest with them through the raging sea. Come, guardian power, whom mortal tribes desire, and far avert the deep’s destructive ire." 
Apuleius, The Golden Ass 4. 31 ff (trans. Walsh) (Roman novel C2nd A.D.) : "Shaggy Portunus sporting his blue-green beard... and Palaemon, the little charioteer on his dolphin."
- [Filippo Coarelli, Guide archéologique de Rome, Hachette, 1994.]
- [Jean Bayet, La religion romaine, Payot, 1999. ]
- [Robert Turcan, Rome et ses dieux, Hachette, 1998.]
- [Georges Dumézil, La religion romaine archaïque, Payot, 2000.]
- [Virgile, Ovide et Varron.]