The river Tiber flows into what arm of the Mediterranean?

The Tiber is the third-longest river in Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing 406 kilometres (252 mi) through Tuscany, Umbria and Lazio, where it is joined by the river Aniene, to the Tyrrhenian Sea, between Ostia and Fiumicino. The Tyrrhenian Sea is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenian people, identified since the 6th century BCE with the Etruscans of Italy. The river has achieved lasting fame as the main watercourse of the city of Rome, founded on its eastern banks.

The river rises at Mount Fumaiolo in central Italy and flows in a generally southerly direction past Perugia and Rome to meet the sea at Ostia. Popularly called flavus ("the blond"), in reference to the yellowish colour of its water, the Tiber has heavily advanced at the mouth by about 3 kilometres (2 miles) since Roman times, leaving the ancient port of Ostia Antica 6 kilometres (4 miles) inland. However, it does not form a proportional delta, owing to a strong north-flowing sea current close to the shore, to the steep shelving of the coast, and to slow tectonic subsidence.