William I, son of Roger II of Sicily and the first king of Naples, built the castle in the 12th century. Frederick II of Hohenstaufen later expanded it and made it one of his royal palaces. The article names no architect, style, materials or dimensions, and gives no date for Frederick's work.
In the 16th century Pedro Álvarez de Toledo consolidated the legal offices there as the Hall of Justice, known as the Vicaria, with prison cells in the basements. The arms of Charles V, who visited Naples in 1535, remain over the entrance. Many restorations followed, one as recent as 1860, and the castle no longer keeps much of its original look.
On August 19, 1432, Sergianni Caracciolo was stabbed there. The City of Naples owns it. The courthouse has moved out, and it is becoming a museum.

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