The New Fortress was built at the western end of the medieval village towards Valdinievole; its wedge shape is due to the morphology of the land. The construction of the New Fortress, also known as Fortress of Castruccio, was decided immediately after the siege conducted by the Florentine and Lucca troops against the castle of Serravalle, the most important system of defense of Pistoia. In 1302 Serravalle was besieged by the Florentine and Lucca armies and was overwhelmed after three months of siege by the troops led by commander Moroello Malaspina. Starting from this period, for about thirty years, the castle became part of the defensive system of Lucca, thus becoming part of the Montecatini – Monsummano – Montevettolini triangle and guaranteed the security of the eastern borders of the territory of Lucca, forming an insurmountable front for the army Florentine. Serravalle and Monsummano accentuated the defensive and military character of their original structure, while Montecatini and Montevettolini combined their military function with a commercial vocation, thanks to the development of various commercial activities within the fortified circuit.
The main gate is on the longer side of the walls. The fortress has walls with internal walkways and two observation turrets at its corners. The walls, originally crenellated, retain the ancient loopholes, which the archers defended the village from. Traces of brick arches appear along them ant they were used to support the walkway. Inside, a rainwater tank is still visible, the only source of supply in the event of a siege. From the construction of the Rocca Nuova came the expansion of the city walls and the new road system of the town.
