There are on the Tiber — in addition to numerous modern bridges — several ancient bridges (now mostly pedestrian-only) that survived in part (e.g., the Milvian Bridge and the Ponte Sant'Angelo) or in whole (Fabricius' Bridge).
The legendary king Tiberinus Silvius, or Thebris, ninth in the king-list of Alba Longa, was said to have drowned in the Albula River, which was subsequently renamed in his honour. The myth may have explained a memory of an earlier, perhaps pre-Indo-European name for the river, "white" (alba) with sediment. According to the legend, Jupiter made him a god and guardian spirit of the river (also called Volturnus, "rolling water"). This gave rise to the standard Roman depiction of the river as a powerfully built reclining river god, also named Tiberinus, with streams of water flowing from his hair and beard. The River Tiber was also believed to be the river into which Romulus and Remus (the former founded Rome) were thrown as infants.
The river marked the boundary between the lands of the Etruscans to the west, the Sabines to the east and the Latins to the south. Benito Mussolini, born in Romagna, adjusted the boundary between Tuscany and Emilia-Romagna, so that the springs of the Tiber would lie in Romagna. Mussolini placed an antique Roman column at the point where the river arises, inscribed QUI NASCE IL TEVERE SACRO AI DESTINI DI ROMA ("Here is born the Tiber, sacred to the destinies of Rome").
The Tiber was critically important to Roman trade and commerce, as ships could reach as far as 100 km upriver; there is evidence that it was used to ship grain from the Val Teverina as long ago as the 5th century BC. It was later used to ship stone, timber and foodstuffs to Rome.
During the Punic Wars of the 3rd century BC, the harbour at Ostia became a key naval base. It later became Rome's most important port, where wheat, olive oil, and wine were imported from Rome's colonies around the Mediterranean. Wharves were also built along the riverside in Rome itself, lining the riverbanks around the Campus Martius area. The Romans connected the river with a sewer system (the Cloaca Maxima) and with an underground network of tunnels and other channels, to bring its water into the middle of the city.
The heavy sedimentation of the river made it difficult to maintain Ostia, prompting the emperors Claudius and Trajan to establish a new port on the Fiumicino in the 1st century AD. They built a new road, the via Portuensis, to connect Rome with Fiumicino, leaving the city by Porta Portese ('the port gate'). Both ports were eventually abandoned due to silting.
Several popes attempted to improve navigation on the Tiber in the 17th and 18th century, with extensive dredging continuing into the 19th century. Trade was boosted for a while but by the 20th century silting had resulted in the river only being navigable as far as Rome itself.
The Tiber was once notorious for its floods — the Campus Martius is a flood plain and would regularly flood to a depth of several metres. The river is now confined between high stone embankments which were begun in 1876. Within the city, the riverbanks are lined by boulevards known as lungoteveri, streets "along the Tiber."
Because the river is identified with Rome, the term "swimming the Tiber" has come to be the Protestant shorthand term for converting to Roman Catholicism. This is most common if the person who converts had been Anglican, the reverse of which is referred to as "Swimming the Thames."