The castle of Groppo San Pietro is a defensive building located in one of the oldest villages in Lunigiana, in the hamlet of the same name in the municipality of Comano. In a key position controlling the garrisons that from the Linari pass descended into the Taverone valley, this castle was built in the Este era around the 12th century. In the 13th century the castle was already part of the Marquisate of Filattiera, while in 1275 it entered the domain of the Marquisate of Olivola.
After its destruction in 1328 by Castruccio Castracani, it fell back into the hands of Spinetta Malaspina, who left it to his grandchildren, marquis of the Verrucola, joining the Florentine Republic in the 15th century.
This area was probably named after a castrensian chapel (which no longer exists) dedicated to the saint. Due to two violent earthquakes, only part of the quadrangular tower, likely from the 14th century, a cistern and some traces of the surrounding walls are visible today.