Question: Which is longer, The Tiber or Cremera?
Context: Cremera is a 36.7 km Italian stream in Lazio (and previously in Etruria) which runs past Sacrofano, Formello, and Campagnano di Roma before falling into the Tiber about 10 km north of Rome.  It connects to the Tiber just as the Via Flaminia intersects the Grande Raccordo Anulare highway, on the proximity of the Labaro Roma Nord railway station, where an ancient Roman bridge is. The Porta Trigemina was one of the main gates in the ancient 4th century Servian Wall of Rome, Italy.  The gate no longer exists, but it is frequently mentioned by ancient authors as standing between the north end of the Aventine Hill and the Tiber River, placing it near the southeastern end of the Forum Boarium.  The Clivus Publicius descended from the Aventine to the Porta Trigemina. Prima Porta is a suburb of Rome located 12 kilometres north of its center along the Via Flaminia and just a kilometre outside of the Grande Raccordo Anulare highway.  It is located on the right bank of the Tiber where the Via Tiberina leads away from the Via Flaminia and another road led off along the Cremera to Veii (Latitude: 42.000992° - Longitude: 12.493380° ).  The location was strategically important due to the iron-rich cliffs of red tuff that approach the river at this point, the confluence of several roads, and its function as the north entry point to Rome.  Parrocchia Santi Urbano e Lorenzo a Prima Porta, is the name of the Catholic Parish.  It is looked after, the location of and serves as a House of formation for the Pauline Fathers. The Tiber ( , Latin "Tiberis", Italian "", ] ) is the third-longest river in Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing 406 km through Tuscany, Umbria and Lazio, where it is joined by the river Aniene, to the Tyrrhenian Sea, between Ostia and Fiumicino.  It drains a basin estimated at 17375 km2 .  The river has achieved lasting fame as the main watercourse of the city of Rome, founded on its eastern banks. The Porto di Ripetta was a port in the city of Rome.  It was situated on the banks of the River Tiber and was designed and built in 1704 by the Italian Baroque architect Alessandro Specchi.  Located in front of the church of San Girolamo degli Schiavoni, its low walls with steps descended in sweeping scenographic curves from the street to the river.  The port no longer exists but is known from engraved views, drawings and early photographs. The Almone (Latin: "Almo") is a small river of the Ager Romanus, a few miles south of the city of Rome.  Today the river is polluted and is channelled to a sewage treatment plant and no longer reaches its natural confluence with the Tiber. Ficana was an ancient city of Latium, which figures in Roman history only on the occasion of its conquest by Ancus Marcius, who is said to have removed the inhabitants to Rome, and destroyed the city itself.  (Livy i. 33; Dionys.  iii.  38, where the editions have "Fidenae", but there is little doubt that the event referred to is the same related by Livy.)  It is certain that it was never repeopled: its name is found in Pliny's list of the extinct cities of Latium (iii.  5.  s. 9), and is noticed also by Festus ("v. Puilia Saxa") as a place no longer in existence.  The latter passage, however, affords us a clue to its position; according to Marcus Antistius Labeo there cited, it was situated on the Via Ostiensis, eleven miles from Rome, and apparently immediately adjoining the Tiber, on which it had a port, at a place called by Fabius Pictor the "Puilia Saxa".  The city's site is in the commune of Rome near Acilia, on the via Ostiense between Rome and Ostia.
Answer: The Tiber