Antiquity Castiglione del Lago stands on a hill that in antiquity formed the fourth island of Lake Trasimeno, before the strip of water separating it from the mainland was filled in.
Middle Ages In the early Middle Ages, Lake Trasimeno marked the boundary between
Lombards and Byzantines. The Byzantines built a large church on the former Etruscan acropolis, dedicating it to Saints James and Philip. In 996
Otto III ceded it to
Hugh, Margrave of Tuscany. According to other accounts, Otto III made Castiglione a fief of the Monks of Saint Januarius of Campolona. After 1000 the settlement was fortified several times in order to control the road leading from Rome and Orvieto toward Arezzo and Florence. Around this time, the town's name evolved from
Castiglione Chiusino to
Castiglione del Lago. In 1091
Henry IV destroyed and burned it. In 1187, by grant made by Abbot Hugh, the Perugians obtained it, though they had to reconquer it because the local population resented the transfer. In 1212
Pope Innocent III confirmed it to Perugia. Even so, it was often contested by Cortona, Orvieto, and Arezzo; it also became involved with Orvieto once Orvieto obtained lordship over Chiusi, in whose diocese Castiglione del Lago was included. In the mid-13th century, Emperor
Frederick II built the large walls that encircle the older urban core. In the 14th century Castiglione del Lago underwent further changes of control, with governments shifting as authority passed between the Church and the Empire. During Perugian civil wars, the Oddi, proscribed by the
Baglioni, found refuge there, though they soon had to withdraw.
Early modern period In the early 15th century Castiglione del Lago was a property of the
Apostolic Camera. In 1515
Pope Leo X stayed in Castiglione del Lago while travelling from Rome to Florence, indicating that the main Chiusian route still passed through the area, linking Tuscany with Perugia. In 1550
Pope Julius III granted the town to his sister Jacoma and to his nephews
Ascanio della Corgna. In 1616
Pope Paul V raised the fief to a duchy in favor of
Fulvio della Corgna. The Palazzo della Corgna was built during this period. The House of della Corgna, first as marquises and later as dukes, ruled until 1647. During this period the town center was reshaped with small houses aligned along two main streets, an urban layout that remains in place. After a poorly sustained siege in 1643, and amid suspicion of secret dealings with the enemy, the della Corgna lost their rights and Castiglione was incorporated into the Papal State.
Contemporary period During the Napoleonic period Castiglione del Lago was the seat of a canton within the
Napoleonic Empire. On 6 July 1816
Pope Pius VII listed it as a community with a resident governor, under the
Delegation of Perugia. In the mid-19th century Castiglione had 6,085 inhabitants, with 1,047 in the main built-up area and 5,038 in the countryside. On 19 October 1860 it joined the newly unified Italian state by vote. == Geography ==