The Church of Santa Maria Forisportam, that is to say built outside of the circle of walls, probably already existed in the second half of the 8th century. It was rebuilt in the 12th century and its upper part was completed in the 16th century.

Inside the church is a sundial of the "camera oscura" type. The light hole is situated up on the eastern wall, while the hour line is traced on the floor. This sundial makes it possible to determine the time by exploiting a beam of light that comes from the light hole. When the light beam encounters the hour line, it means that the Sun has reached its maximum height, thus indicating when it is truly 12.00 noon in the place (7’55" behind the solar time of Rome).