The original entrance door of Palazzo Costaguti is walled-up. In old times, Via della Reginella was one of the streets of the Jewish ghetto and the rules said that every door here had to be closed during the night-time. For this reason, the owner of the building decided to wall-up that entrance and to open another door facing right out Piazza Mattei. The original entrance, still walled-up, can be seen today.