The fourth tower from Porta San Giovanni was no longer used for defensive purposes from the Middle Ages onwards, when a very important place of worship and prayer, dedicated to St Margaret of Antioch, was established within it. The room on the ground floor of the tower was renovated and possibly used for worship as early as the 13th century, but it was not until the following century that it was completely renovated, and its walls and ceiling were decorated with frescoes. These frescoes, dated to the first half of the 14th century and attributed to the school of Pietro Cavallini, show a series of saints, deacons and religious scenes, including Saints Peter and Paul, the martyrs Stephen and Lawrence, Saints Margaret and Catherine and other scenes depicting the Madonna and Child, Christ and the Annunciation. The paintings, badly damaged by the humidity at the site, were removed in the 1970s and are now on exhibit in the museum of Santa Croce in Gerusalemme, which can be visited upon request. The upper floor of the tower, now inaccessible, has been subjected to numerous alterations over time.
2. Santa Margherita Oratory. Exterior.