The fortress was built on the highest point of Montecarlo hill, known as the "Cerruglio". Its strategic position between the valleys of Lucca and Valdinievole, made it desired by the most powerful cities of Tuscany: Florence, Pisa and Lucca. For this reason it has been the site of numerous battles and the structure of the fort has undergone many changes over time. Castruccio Castracani (which led the Lucchese army against the Florentine guelphs during the battle of Altopascio), Popes and Kings passed by.
The Montecarlo Fortress is made up of a tower and two square towers connected to each other by high walls that form an imposing triangular structure.
The "fortezza" became private property in 1775, when Grand Duke Pietro Leopoldo of Tuscany, who did not consider it useful to military purposes anymore, disarmed it and sold it. Further conservation and restoration works of the whole structure are carried out by current owners in order to keep the original appearance as much as possible and to make it available for visitors as an exhibition centre where shows, conventions and other cultural events are held.