Monsummano Castle, Medieval fortification in Monsummano Alto, Italy.

Monsummano Castle is the oldest nucleus of Monsummano, now centred on Monsummano Terme. It occupies an elliptical hilltop at 340 metres, coinciding with the village of Monsummano Alto. Wide stretches of the original two-kilometre circuit of walls survive, partly hidden by vegetation, with two original gates: Nostra Donna to the north-west and Del Mercato to the north-east.

A first, uncertain documentary mention dates to 1005, when Abbot Boso of Sant'Antimo sold half a castle near the old church of San Vito on the Nievole to Count Ildebrando di Rodolfo degli Aldobrandeschi. In 1218 Abbot Ugone of Sant'Antimo sold the castle with all its appurtenances to the commune of Lucca. Florence occupied it in 1314, Castruccio Castracani retook it on 29 August 1315, and Florence regained it in 1331.

The church inside the walls is dedicated to San Nicolao, not San Niccolo, and shows Romanesque-Gothic forms with later alterations. A chapel annexed to it now houses a restaurant, and a small cemetery with its own chapel stands among the ruins of other buildings.

The site is reachable via highway A11 at the Montecatini exit, then follow signs to Monsummano Terme and continue uphill to the ruins. Wear sturdy shoes as the paths to the walls and gates are uneven, with some sections running across open terrain.

Only one tower survives: a pentagonal structure with a single raised entrance about seven metres above the ground, reached originally by a wooden staircase that could be removed in case of attack. Recently restored, it is considered one of the finest in the area.