The Rocca had great strategic importance throughout the Middle Ages, controlling trade on the lake, and was also a residence of the archbishops of Milan, until in 1384 Caterina Visconti, wife of Gian Galeazzo, obtained the Rocca from the Pope as a possession of the family.
When the Visconti lost the Dukedom of Milan in 1449, the Rocca was granted to Vitaliano Borromeo, and for centuries the fortress and a large part of Lake Maggiore were strongholds of the Borromeo family. Since the 19th century, with the loss of its military importance, the medieval fortress gradually began to be used as seat of cultural and artistic events.
The large construction is surrounded by high walls with Ghibelline merlons and corridors at top of the walls for the soldiers, interrupted by a huge tower, with the side facing the lake inaccessible, descending almost vertically down to the lake bank. Inside the walls is the outer courtyard, which leads to a second defense wall, accessible in origin only through a no more extant moving bridge. A gate in the tower then leads into the U-shaped inner courtyard, where the main residential complex is located, with a fine covered belvedere over the lake. The Cortile nobile, or inner courtyard, leads to the main residential part of the Rocca; the construction goes back to the 13th century, and is called "Ala Scaligera" since it was greatly renovated under Regina della Scala, the wife of Bernabò Visconti, in the 1370's. To the left of the construction is the huge tower, the main feature of the Rocca profile, originally consisting of five levels, of which only three are extant, and still to the left the Visconti Palace, built in huge square, regular stones at the time of Ottone Visconti, who was made archbishop of Milan in 1262. The ground floor is divided into different sections by 3 huge 8-sided columns, decorated with beautiful capitels. To the south of the inner courtyard is the Borromeo Wing, renovated in the 15th and 16th centuries, with an elegant Renaissance lodge.
This section hosts the Museo della Bambola (=dolls' museum), established in 1988, the first in Italy and among the most representative in Europe, which originally consisted of a collection of the Borromeo family, but was greatly enlarged in later decades to include dolls and toys of all ages and places, as well as dolls' clothes and furniture. Attached to the Museo is also a collection of children's clothes of the 19th century.
The Sala di Giustizia The huge local, situated at the ground floor of the main Tower, is separated by arches into two vaulted rooms, and decorated with an exceptional fresco cycle, with scenes separated by geometrical motifs. The central levels of the frescoes on the walls describe events of the fights and victory of Archbishop Ottone Visconti (1205-1295, the founder of the Visconti rule on Milan) on Napo Torriani. On the right wall is a fresco which was originally in the Oratory of St Bartholomew, a chapel in the castle, representing the Virgin with Child. From the Sala a wooden stairway leads to the upper floors of the Tower, which offer a splendid panorama on the lake and its hinterland.
The Ala Borromea - This wing contains frescoes detached from the Palazzo Borromeo in Milan, among them a beautiful "Raccolta delle Melograne" (=Pomegranate Harvest) and scenes from the Fables of Aesopus. Other rooms contains portraits of personages and events of the Borromeo family
The Lapidario - under the Lodge an exhibitions of Roman artifacts, among them altars and a fine decorated basement of a statue to Jupiter Optimus Maximus.