The Sacco is a river of central Italy, a right tributary of the Liri. It flows between the Metropolitan City of Rome Capital and the province of Frosinone in Lazio.

The river originates from the Prenestini Mountains,^[1] formed by the confluence of two streams of the Monti Simbruini in the Apennines of Abruzzo in Lazio, and flows south-east for a total length of 87 km,^[1] crossing the Middle Latin valley between the Ernici Mountains to the northeast and the Lepini Mountains to the southwest; at the height of Ceprano it flows into the Liri River from the right.^[1]

The Sacco's main tributaries are the Cosa and the Alabro.

In old sources, it is known also the Tolero,^[2] from its ancient name Tolerus or Trerus.

The Sacco river valley is a vast territory between the provinces of Rome and Frosinone in the central-southern Italy. The intensive exploitation that for decades affected of this valley due to no-scruple companies and crooked public administration offices, produced an unprecedented environmental and social disaster.^[3]