Among the numerous fortresses that are scattered throughout the Casentino, the castle of the Guidi of Poppi is the one that has kept its ancient structure until our days. Inside, it houses the "Rilliana" Library, with a collection of medieval manuscripts and incunabula, and the "Chapel of the Counts", decorated with a precious cycle of XIV-century frescoes attributed to one of Giotto's pupils.
The castle was the house of the Counts Guidi for more than four hundred years. This family of powerful feudatories depending upon the emperor had kept many estates in a wide part of Tuscany since before the year 1000 until the great battles between the Guelfs and the Ghibellines in the XIII-XV centuries. The first certain news on the castle dates to an imperial act by Henry IV issued in 1191 to confirm the seigniory of the Guidi on it, but many think that its first building dates to the IX century or even before.
Initially, the stronghold of the Guidi was constituted of the square tower that still overlooks it. This tower was restructured and transformed into a belfry after the damage of the XIX century caused by a lightning. This makes also think that it was probably higher than it is today. Part of the complex is filled with earth today. Its walls are more recent since they were finished around the half of the XIII century.
The rectangular complex that raises near the tower was also added later and joined to it through walls. At the beginning, they were separated so to be independent when they were attacked. Still in the XIII century, the forecastle and the courtyard were completed and they gave the complex its mainly residential characteristics. In 1440, the castle was the scene of the Counts Guidi's surrender to Florence. They wrote the treaty with which they ceded Poppi to their Guelf rivals right in these rooms.
The last great works on the castle were carried out around 1470 and they altered its structure by transforming the secondary entrance into the main door called "Porta del Leone". The inner door called "della Munizione" was raised to defend the main door and a drawbridge, that does not exist today any more, was built. In the XX century, the castle required restoration works that could take it back to its ancient beauty, even if it never deteriorated seriously.