The church of St Peter is located on the highest part of Segni which once was the acropolis of the city and is probably on the site of the pagan temple. On the stone walls of the church we can recognize in the low parts polygonal walls followed by different layers of stones with different structures that correspond to different eras.
The church is accessed via a wide paved walkway that leads to a simple facade with a Romanesque door, two circular openings and a gabled roof. Next to the church is a Romanesque bell tower, also on a foundation of a previous construction, which ends with a single window.
The interior is a nave decorated with a fresco of the twelfth century that represents a Madonna with Child and two others represent St. Sebastian and the Virgin enthroned between Saints Lorenzo, Stephen and Vitaliano.
Among the other works there is a painting from the 1500s and an altarpiece made by Tadolini in 1907.