The name Bibbiano is derived from “Bibbio” (“bibianum” in Latin), a name of the Eurasion widgeon: an aquatic bird, similar to a duck, that once abounded in this area. The castle was owned by the Guiglieschi family until, in 1051, the Emperor Henry III put it under the control of the Abbey of Sant’Antimo. Bibbiano next passed into the hands of the counts of Cacciaconti who, in 1197, gave it to the Sienese Republic. It was at this stage that the reinforced structures were put in place. Further additions and restorations were carried out in 1338 and 1400, during which time Pietro Lorenzetti guested here and painted his last work, L’Annunciazone. At the start of the sixteenth century, having been damaged many times, the complex was acquired by Cardinal Raffaello Petrucci and was restored by Baldassare Peruzzi, who painted a splendid Madonna in its chapel. At various times the castle changed hands between Siena's Borghesi, Chigi and Malavolti families, and in 1922 it was declared a “National Monument”.