The historic center of Castiglione del Lago has several elements that make it unique in the architectural panorama of Umbria. Commissioned by Frederick II, between 1247 and 1250, Brother Elia da Cortona transformed the small fishing village, surrounded by walls and with a tower on top of the promontory, into a real castle-town that closed towards the lake with an impregnable fortress. The hill where the town stood was flattened and leveled, powerful external walls were built starting from the base of the hill, so that the level of the historic center is over 20 meters higher than that of the base of the walls. Here there were 3 gates, with 3 streets and 3 squares. The keep was also built with only 3 sides, to give prominence to the number 3 indicative of the Holy Trinity.
