Because of its location, the Montesummano castle played an important role in the 13th-century conflicts between Pistoia and Lucca, with the boundary between the two important communes being specifically defi- ned at the end of the century. In the 14th century, Lucca recognized the castle's strategic importan- ce by including obligations for the castle's defense in its statutes.
Already established as a rural community in 1216, Monsummano fought against Florence in 1328 in the Valdinievole's league of castles. The following year, it joined forces with the Florentine Signoria. In 1331, the first Florentine podestà settled in Monsummano and Florence recognized Monsummano's communal statutes. Despite this formal recognition, the 1329 alliance with the Florentine Signoria was an act of submission.
The ancient castle's elliptical circuit of walls has been almost entirely preserved, stretching for about two km. Its western end is marked by ruins of the large pentagonal tower that, in its present form, dates from the early 14th century.
Known as 'Nostra Donna' ('Our Lady'), the gate allowed access to the castle from the northwest. On the opposite side is the almost undamaged 'Porticciola' or 'Porta del Mercato' ('Market Gate') that still today faces Montevettolini, a striking backdrop for the breathtaking panorama that opens on to the valley.
Most inhabitants lived inside the castle with the houses likely clustered in the middle. There were vegetable gardens along the inside walls. There was the only parish church, the church of San Nicolao. Founded in the 11th century, it served as the parish church until 1731.
The castle began to lose strategic importance after the entire Valdinievole came under Florence's dominion, especially following the change in grand ducal policy toward the Fucecchio Marsh, between the late 16th and early 17th century, which favored the formation of a Monsummano Basso settlement.