In the 15th century the so-called Castelletto was built, dependent on the Malatesta Fortress above it. This was the seat of the Banco della Ragione, that is, the Court of Civil and Criminal Justice, and also the seat of the Office of Notaries who dispensed the various legal acts. The palace had attached to it the title of Count, intended for its rightful owner. It was one of the last counts who rendered the structure in its present form: law doctor Antonio Maria Marcosanti, who renovated the palace in lavish form. In 1748 he had a small but elegant oratory dedicated to St. Francis of Paola built on the left side. When Count Antonio Maria Marcosanti died, the palace passed to his daughter, who married a Nardini from San Leo. This Nardini thus became the owner of the building, also inheriting his title of count. The palace, in 1789, was the seat of a Scientific and Literary Academy. In the basement of the palace there are still tunnels, caves and dark corridors that, together with the few remains of the castle rampart, represent what remains of the Malatesta fortress of Sogliano.