Castello dell'Aquila belongs, and with great dignity, to that set of fortresses, fortified buildings, watchtowers that made Lunigiana a unique territory of its kind. From the top of a hill it dominates the medieval village of Gragnola, an inhabited place at the confluence of the Aulella and Lucido creeks. The origins of the fortified settlement on the hill are uncertain, probably to be related to the control over the medieval transits that reached Rome from central Europe, crossing at the road junction of the village below. According to some historians, Gragnola is Forum Clodi, a place reported in the oldest "European road atlas" that history remembers, known as the Tabula Peutingeriana and dating back to the early centuries of the early Middle Ages.

The first fortified structure was perhaps built by ancient local nobles between the ninth and tenth centuries, the Bianchi d’Erberia. The castle and its fiefdoms passed to Spinetta II the Great in the period that coincided with its expansion largely in the eastern Lunigiana, or between 1327 and 1352, the date of his death.

Two are the dynasties of marquises that took their name from Castel dell'Aquila, both coming from the Malaspinian branch of Fosdinovo: the first originated from Galeotto di Fosdinovo in the fourteenth century, the second began with Lazzaro, son of Antonio Alberico marquis of Fosdinovo, whose lineage died out in the first half of the 17th century.

Among the latest significant changes there is the construction of the external walls, between the 15th and 16th centuries, by the new marquises of Castel dell’Aquila to adapt the now obsolete medieval defenses inadequate to firearms. Access to the castle was totally changed with the addition of a round turret and a barbican and other defensive devices. In practice, access to the castle was transformed into a corridor from which it was almost impossible to deviate. The political and economic decline of the Malaspina led to the abandonment of the Castle.

It is the twentieth century, however, the dark century of the Castel dell’Aquila, damaged by an earthquake in 1920 and years of neglect, abandoned after the last owners undermined the tower, then unsafe, with dynamite. It took two years to free it from the brushwood, ten to bring it back to its original grandeur, thanks to an important restoration work carried out with passion by the current owner.

During the works, studies were carried out which made it possible to understand the various stages of development of the settlement and the subsequent changes made over the centuries.

Now Castello dell’Aquila appears to us as a powerful monolithic structure that includes the quadrilateral main tower and three other corner towers. The north-west tower houses a door that was the access to the internal courtyard before the Renaissance changes. In the atrium, immediately on the right, we find the chapel. All the residential buildings overlook the internal courtyard, still partially adorned to the north by Guelph battlements. Among these, the large hall on the opposite side of the entrance with a barrel roof deserves to be mentioned; the main tower which dates back to the thirteenth century, at least in its oldest part and the sixteenth-century addition, now a residential part of the structure. The rest of the castle can be dated essentially to the 14th century, when it became the seat of the Marquisate and took the title of Castel dell’Aquila.