Little is known about the worship of Tiber (Tiberinus), which is very old, but Ovid recalls seeing games named after the river Tiber held on the Campus Martius. Festus records that the Ludi Piscatorii (June 7) were conducted by the city praetor on behalf of the fishermen of the Tiber. The celebrations were likely held on both banks of the river. The fish caught that day were not taken to the market but to the precinct of Vulcan where they were thrown live on the fire as substitutes for humans. This curious procedure has been construed to be an offering of creatures that would ordinarily be safe from the god of fire in exchange for things that might easily catch fire in the heat of June.

According to tradition, the Tiber was originally called Albula and received the name Tiberis after the death of the king of Alba, who drowned in it. The river arises from two springs in the Apennines, near Trifernum, and flows in a southwesterly direction, separating Etruria from Umbria. Within the walls of Rome, the river is about 300 feet wide and from 12 to 18 feet deep. After heavy rains, the river frequently overflowed its banks and did considerable mischief to the lower parts of the city. Roman poets often referred to it as flavus Tiberis because its waters are muddy and yellowish.