[1] Its wide dimensions induced Petrarch, who visited Pavia in the fall of 1365, to call it "an enormous palace in the citadel, a truly remarkable and costly structure".

His idea to build a castle came from Pavia's ancient role as the capital of the Lombard Kingdom and the Visconti's ambition to extend their dominion to its territory.

Some details, such as the internal square module and the four-light windows, have tentatively identified the Venetian architect Bernardo da Venezia, who was nevertheless active in Pavia only after 1389.

The Sala grande dele caze (Great Hunting Hall) occupied three square modules on the first floor and was the most prominent room in the castle.

He directed frequent military campaigns against the nearby local powers from the castle, making Pavia the capital of a continuously increasing territory.

[24] The western tower hosted the Visconti Library, a vast collection of books gathered by Galeazzo II and expanded by his son.

Pisanello worked in Milan in 1440, and Filippo Maria Visconti (the son and successor of Gian Galeazzo) asked him to paint the great fresco later attested in one of the castle's rooms.

Before the Galeazzo Maria Sforza's marriage to Bona of Savoy in 1468, Bembo was again called in Pavia to renew the existing frescoes.

The following year, claiming hereditary rights against the Sforza house, he invaded the Duchy of Milan and occupied Pavia.

Francis I, the successor of Louis XII and Valentina Visconti's descendant, defeated the Sforza in the Battle of Marignano in 1515 and conquered Milan and Pavia again.

The French encountered the opposition of the emperor Charles V, who defended the imperial role as the grantor of the Duke of Milan title.

[42] In the portico on the ground floor there are traces of the first pictorial decoration with geometric figures, while on the vaults the starry sky was painted, ordered by Galeazzo II for the whole castle in 1366.

Some doors open onto the portico still retain the inscription in Gothic characters which identified the entrance to rooms used as offices, including the one intended for the accountancy of the Duchess Caterina Visconti.

[46] On the ground floor of the south-west tower is the "blue room", the result of the pictorial interventions of 1469, particularly sumptuous for the preciousness of the techniques and materials used.

The decoration is made up of squares with raised and gilded frames, which divide the walls, always in relief and covered with gold foils are the heraldic motifs (lilies of France and Sforza emblems) and stars, on alternately blue and green backgrounds.

On the ground floor, immediately to the right of the southern entrance, there is the chapel, with a rectangular plan and rib vaults, on the portal of the chapel there is a sinopia depicting the Pietà, by Michelino da Besozzo,[47] while inside there are frescoes, such as Geometry or The Blessing Christ, by Andrea da Bologna.

[48] Also in the chapel, the two Saints Stephen and Leonard, painted within the squares, facing each other, on the piers of the arch that divides the room into two bays, were executed at a later time, however in the last quarter of the Three hundred, and are the work of a Lombard master.

Also on the ground floor is the "room of the doves" where on a reddish background the Visconti devince of the Colombina alternates with the motto "à bon droit", adopted by Gian Galeazzo, and that of the mountain with the three pine cones and the motto "mit Zeit ", these frescoes, like those in the" blue room ", date back to the interventions of 1469.

On the first floor (the noble floor, where the ducal apartments were located, the library, in the tower at the southwest corner, and the chancellery, south-east tower, of which the inscription on the door is still preserved) there is the "room of the bridesmaids" where there are two frescoes, depicting life-size ladies in front of a hedge of roses dating back to the pictorial interventions promoted by Gian Galeazzo in 1393 and recently attributed to Gentile da Fabriano, who in those years worked in Pavia.

[49] In the internal courtyard, on the side where a wing and two towers are missing for the 1527 artillery attack, the remains of the Spanish Walls are visible.