Sarthe is a river in western France. Together with the river Mayenne it forms the river Maine, which is a tributary to the river Loire. Its source is in the département Orne, near Alençon. It flows through the départements Orne, Sarthe and Maine-et-Loire. It flows through the cities Alençon and Le Mans. A few km after its confluence with the river Loir, it joins the river Mayenne, north of the city Angers.