he Pietra di Bismantova is a geological formation in the Reggiano Apennines, in the comune of Castelnovo ne' Monti, province of Reggio Emilia, central Italy, c. 45 km from Reggio Emilia.
It has the shape of a narrow, quasi-cylindrical plateau (measuring 1 km
x 240 m) whose steep walls emerge c. 300 m as an isolated spur from the
nearby hills. The top has an altitude of 1,047 m over the sea level. It
is included in the National Park of the Appennino Tosco-Emiliano.
The spur is composed of yellowish calcarenite over a marl basement, all formed in the Miocene as a sea bottom. It includes fossils belonging to a tropical environment. It is surrounded by woods, mostly of oaks.
The Pietra di Bismantova is mentioned by Dante Alighieri in his Divine Comedy (Purgatory, IV, 25-30).