This Cathedral (Saint Gregory the Great) was built in 1666 by Pope Paul V Borghese in honour of Pope Gregory who had signed the papal bull of the Gregorian Calendar here. The design and construction was by Girolamo Rainaldi. The façade, which looks directly at the valley, has two towers on each side and is characterized by rigid geometrical designs. The plan of the cathedral is a Greek cross and inside there are paintings of the seventeenth century. In the basement of the church the remains of a Roman villa have been found above which was born Monteporzio.