Since Etruscan times, the area around Castiglione del Lago, under the dominion of Chiusi, has concentrated mainly on agriculture, especially the production of grain. There is plenty of evidence for this in the many agricultural finds in the area.

Around the 7th century, Castiglione's promontory and peninsula provided the Tuscia Lombards with a formidable defensive position against Byzantine Perugia. The town wasfought over by Arezzo, Cortona and Perugia, Perugia finally running out the victor.

ln 1247, Frederick II of Swabia conquered the town and rebuilt it in the form in which it can still be seen today. The Emperor probably used the skills of Father Elia Coppi of Cortona, who created a regular street plan divided into six square sections, served by three streets, three squares and three gates.

This Franciscan friar was also the architect of the Rocca del Leone (Lion Fortress), in the form of a pentagon withfour corner towers and a keep on a triangular plan. The building, one of the finest examples of medieval military architecture in Umbria, is situated on a spur of limestone rock which gives it complete dominion over Lake Trasimeno.

A delighiful covered walkway connects the fortress to the Renaissance Della Corgna Palace, built for Ascanio della Corgna, who in 1563 received the title of Marquis of Castiglione del Lago and Chiugi from his uncle, Pope Julius III del Monte.

The interior of the Palace, designed by the Perugian architect Galeazzo Alessi, is extensively decorated with frescoes, many of them by the Tuscan painter Niccolò Circignani, known as "Il Pomerancio".

Isola Polvese, the largest island in the lake, also belongs to Castiglione del Lago.
Half the island is covered with a thick growth of ilex, and half with extensive olive groves.

lt became Perugia's first dominion in the Trasimeno area, in 1139.
Particularly noteworthy are the 15th century Abbey of San Secondo, the Castle and the Church of St. Julian.