Lake Fucino was once the third largest lake in Italy. Just east of Avezzano, about 600 m high in the Marsica area of the Abruzzo mountains, it was fed by the melting snows and springs of the surrounding mountains and covered some 150 sqm. Estimates of the seasonal change in water level suggest it fell as much as 12 m, leaving large areas of mud exposed in the process.

It was trapped there, separated by mountains from the Liri valley to the south and the Peligna valley to the east, and by rising land near the headwaters of the Turano and Salto rivers to the north-west. To the north lay the uplands of Abruzzo, now with the modern ski resorts of Ovindoli and Campo Felice.