The Foglia (also called Isauro, e.g. in Belforte all'Isauro) is the northernmost river of the Marche region of Italy.

In ancient times it was known as Pisaurus,[1] as it debouched into the Adriatic Sea at Pisaurum (modern Pesaro).

[2] The source of the river is west of Sestino in the province of Arezzo (which is in the Tuscany region of Italy) in the Umbrian-Marchean Apennines mountains.

The river meanders south of Montecalvo in Foglia before curving northeast and flowing near Colbordolo, Saludecio, Sant'Angelo in Lizzola, Montecchio, Montelabbate and Tavullia before entering the Adriatic Sea near Pesaro.

The river, originally known as Isaurus, marked the boundary of the territory of the Piceni Italic tribe.