The Castle of St. George (Castello di San Giorgio) was built from 1395 and finished in 1406 under commission by Francesco I Gonzaga, designed by Bartolino da Novara, one of the most renowned military architects of the time. It has as square plan with four corner towers, surrounded by a ditch with three entrances, each one with a drawbridge. In 1459 architect Luca Fancelli, commissioned by marquis Ludovico III Gonzaga, who assigned several rooms of the Corte Vecchia for the Council of Mantua called by Pope Pius II, restored the castle, which lost definitely lost its military and defensive function.
References:Rosenborg Palace was built in the period 1606-34 as Christian IV’s summerhouse just outside the ramparts of Copenhagen. Christian IV was very fond of the palace and often stayed at the castle when he resided in Copenhagen, and it was here that he died in 1648. After his death, the palace passed to his son King Frederik III, who together with his queen, Sophie Amalie, carried out several types of modernisation.
The last king who used the place as a residence was Frederik IV, and around 1720, Rosenborg was abandoned in favor of Frederiksborg Palace.Through the 1700s, considerable art treasures were collected at Rosenborg Castle, among other things items from the estates of deceased royalty and from Christiansborg after the fire there in 1794.
Soon the idea of a museum arose, and that was realised in 1833, which is The Royal Danish Collection’s official year of establishment.