Castiglione del Lago has evolved on what used to be an island – the fourth island of Lake Trasimeno, in its south west region. Over the centuries, as the town grew, the flat gap between the island and the shore was filled with piazze, houses, churches and other buildings.
The newest parts of the city are at some distance from the old, so the centro storico (historical center) of Castiglione del Lago is a well preserved medieval locality that seems to be governed by a “law of threes”. In the town walls there are three gates, and inside the town there are three piazze and three churches.
Castiglione lies on the once important highway between Orvieto to the south, Chiusi to the west, and Arezzo to the north. Its position in this hotly disputed territory, pitting Etruscans against Romans, and later Tuscans against Perugians, inevitably brought a long cycle of death and destruction to the town. The original fortifications were destroyed and rebuilt on numerous occasions.
It was only during the reign of Emperor Frederick II (early 13th century) that a period of relative stability ensued. Later the city fell under the control of Perugia, within the Papal States, becoming the fiefdom of the powerful Baglioni family. In 1550, Pope Julius III bestowed it upon his sister.
In 1563, her son, Ascanio della Corgna, became the Marquis of Castiglione and Chiusi. The fiefdom became a prosperous, but short-lived Duchy in 1617. Duke Fulvio Allesandro died without heirs and the town was re-absorbed into the Papal States.