The Onano castle was built around the first half of the fifteenth century by the Monaldeschi as an austere and elegant building. It is almost square and decorated with rectangular battlements of the Guelph type. In the first half of the sixteenth century a high tower was built to which in the late sixteenth century a further addition was made. Originally there was a moat in the Fortress square and a drawbridge as a last defence of the castle itself. In the second half of the eighteenth century it was obtained by the Denham family and its other name, Palazzo Madama, comes from Madame Carlotta Denham. From 1870 to 1908, the Pacelli family owned the castle and here Eugenio Pacelli, the future Pope Pius XII, spent his childhood summers. Today the castle is the town hall.