San Crisogono in Trastevere is dedicated to the martyr Saint Chrysogonus. It was probably built in the 4th century under Pope Silvester I (314–335), rebuilt in the 12th century by John of Crema, and again by Giovanni Battista Soria, funded by Scipione Borghese, in the early 17th century.
The bell tower dates from the 12th century rebuilding. The interior of the church was rebuilt in the 1620s on the site of a 12th-century church. The 22 granite columns in the nave are reused antique columns. The floor is cosmatesque mosaic, but most of it is hidden by the pews. The confessio in the sanctuary area is from the 8th century. The high altar is from 1127, with a baldachino from (1627 or 1641) by G.B Soria.
Remains from the first church, possibly from the reign of Constantine I, and earlier Roman houses can be seen in the lower parts, reached by a staircase in the sacristy. The ruins are confusing, but you can easily find the apse of the old church and you can see the remains of the martyr's shrine in middle of the apse wall. The church had an uncommon form; rather than the normal basilical plan with a central nave and two aisles on the sides, it had a single nave.
The paintings are from the 8th to the 11th century, and include Pope Sylvester Capturing the Dragon, St Pantaleon Healing the Blind Man, St Benedict Healing the Leper and The Rescue of St Placid.
Several sarcophagi have been preserved here, some beautifully decorated.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.