The Tiber (in Latin: Tiberis) is a river in Italy which, according to myths, was the place where the city of Rome was founded on, and whose god was Tiberinus (incidentally, the name of the ninth king of Alba Longa, who was said to have given the river, originally called Albula, its name, after drowning in it).
Tiberinus, the god of the river Tiber, helped Aeneas in his travel from Troy, suggesting to him that he land in Latium. Legend says Rome's founders, the twin brothers Romulus and Remus, were abandoned in a basket on its waters, where they were rescued by a she-wolf, Lupa. Later Romulus founded the Roman Kingdom on the Palatine Hill, by the shore of this river. It was considered one of the most important rivers in the whole kingdom. The Tiber was also fast flowing, even at the end. During ancient times, starting in the later reign of emperor Tiberius, criminals executed on Gemonian stairs were then tossed into the mouth of the Tiber, which was many kilometers southwest of Rome.
The Tiber river is the third longest river in Italy, the river has achieved lasting fame as the main watercourse of the city of Rome, which was founded on the Eastern banks. Popularly called flāvus, the blonde, in reference to the yellowish color of its water.
Just as Rome was founded on the shores of the Tiber River, there is a similar river that has followed the Roman beliefs to Camp Jupiter, a training ground for Roman demigods. The river is called the 'Little Tiber' mentioned several times throughout the book.
Percy and Annabeth have lunch on the Tiber.