Prato, Castle of the Emperor
The fort of the Alberti di Prato once stood on the site where the present castle is located, which was almost completely razed to the ground in 1107 during the siege of the troops of Matilde di Canossa; in its place another palace, called "Palazzolo", was rebuilt to house the nuncios of the emperors Arrigo VI of Svevia and Otto IV of Brunswick (of which two towers remain, those without battlements, which until 1767-68 had about the double the current height); the area affected by the Castle has always been strategic, so much so that there are documents dating back to 1035 which testify to the presence of an older "palatium"; this building was the nucleus of Castrum Prati, the village that stood upstream of the building which also possessed an ancient parish church (Santa Maria in Castello, which no longer exists). The commission for the construction was given by Frederick II to Riccardo da Lentini, probably starting from 1240. The castle, originally tangent to the second walls (XII century), was partially surrounded by a moat and connected to the Albertian prisons from which definition " of the prisons "the nearby Marian shrine took its name. It has eight towers and has inherent, as for the Castel del Monte, various symbolic aspects, both in the structure and in the portal. Once completed it should have been used as an important garrison of the empire, testifying to the presence of the emperor on the possessions of the north. However, its construction was interrupted around 1250, due to the premature death of the emperor, and the unfinished structure was later used for many other purposes. During the fourteenth century, under the Florentine dominion, the castle was connected to the third circle of walls by a covered corridor called "Corridore del Cassero" (ie: corridor of the castle) or more simply Cassero. In this way the Florentine troops could easily enter the city from outside the walls using a protected passage.