What major river runs through Rome?

The Tiber is the third-longest river in Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing 406 kilometers (252 mi) through Umbria and Lazio.  It drains a basin estimated at 17,375 square kilometers (6,709 sq mi). The river has achieved lasting fame as the main watercourse of the city of Rome, founded on its eastern banks.

According to legend, the city of Rome was founded in 753 BC on the banks of the Tiber about 25 kilometers (16 mi) from the sea at Ostia. The island Isola Tiberina in the center of Rome, between Trastevere and the ancient center, was the site of an important ancient ford and was later bridged. Legend says Rome's founders, the twin brothers Romulus and Remus, were abandoned on its waters, where they were rescued by the she-wolf, Lupa.

Because the river is identified with Rome, the terms "swimming the Tiber" or "crossing the Tiber" have 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" or "crossing the Thames."

In ancient Rome, executed criminals were thrown into the Tiber. People executed at the Gemonian stairs were thrown in the Tiber during the later part of the reign of the emperor Tiberius. This practice continued over the centuries. For example, the corpse of Pope Formosus was thrown into the Tiber after the infamous Cadaver Synod held in 897.