Sismano or Sosmano was described, in the 1322 historic archive of Todi, as a castle of "twenty one fires" and was considered one of the many fortresses that guarded the city of Todi. In 1254 Sismano endured large damage due to the harsh battles between Guelfi and Ghibellini, and the feuds between Todi, Florence, Narni and Spoleto. Between 1281 and 1294, the Cardinal Benedetto Caetani spent long periods of time in Todi trying to pacify the disputes between the party of the guelfe cities of Todi, Perugia and Spello and that of the ghibellina city of Foligno. In 1289, through the Florentine merchant Mainetto di Rinaldo dei Pulci, the Caetani Cardinal had the opportunity to buy the castle of Sismano for 8,500 gold florins. The Cardinal was able to visit Sismano on a regular basis during the periods of suspension of the Conclave of Perugia in which, on the 5th of July 1294, Pietro del Morrone with the name Celestino V was made Pope. However, he abdicated the 13th of December of the same year, during the gathering of the Concistoro in Naples. Nine days later, the Cardinal Benedetto Caetani became Pope with the name of Bonifacio VIII. Still today on the sides of the arch, found inside the Borgo, it is possible to admire the two coat of arms of the Caetani family that represent two oblique waves on a shield. The Comune of Todi had jurisdiction on Sismano until he 1st of December 1383 when the Pope Urbano VI conceded it to the Atti family who owned it in alternated phases until the end of the 1500: as a matter of fact, in 1406 the nobleman Giacomo Guglielmi resided in the castle, followed by Matteo Chiaravalle in 1462 who occupied Sismano unlawfully. Eventually it was returned to Ludovico Atti. The coat of arms of the Atti family is located in the middle of the same arch that displays the coat of arms of the family of Bonifacio VIII on its sides. The properties of the Atti family were confiscated by the Pope in the second half of the XVI century due to the massacre commanded by them at the near by castle of Casigliano to damage the Cesi family. The 10th of April 1607, Bartolomeo Corsini bought the estate of Sismano, which, still today, is owned by a heir of the same family.