Built outside the walls to the north of the walled enclosure, San Martín Church has a Roman origin, as confirmed by the latest archaeological explorations. After the Roman building had been apparently ruined, it was rebuilt and radically transformed in the 16th century and at the beginning of the 18th century.
In the 14th century, the tower was built on a base made of granite ashlar work and an upper body made of brick. It also stands as a belfry of Gothic tradition and shows evidence of the Mudejar Masters. The pointed openings are of particular interest and are made of decreasing horseshoe archivolts set in a panel.
In the 16th century, the layout was completed and structured into three naves separated by semi-circular arches. In the 18th century, the Main Chapel was refurbished and the side chapel and semi-spherical cupola above the Presbytery were built. Two Roman altar stones were reused in the south wall.References:
The Basilica of Santa Maria in Trastevere is one of the oldest churches of Rome. The basic floor plan and wall structure of the church date back to the 340s, and much of the structure to 1140-43. The first sanctuary was built in 221 and 227 by Pope Callixtus I and later completed by Pope Julius I.
The inscription on the episcopal throne states that this is the first church in Rome dedicated to Mary, mother of Jesus, although some claim that privilege belongs to the Basilica di Santa Maria Maggiore. A Christian house-church was founded here about 220 by Pope Saint Callixtus I (217-222) on the site of the Taberna meritoria, a refuge for retired soldiers. The area was made available for Christian use by Emperor Alexander Severus when he settled a dispute between the Christians and tavern-keepers.
The church underwent two restorations in the fifth and eighth centuries and in 1140-43 it was re-erected on its old foundations under Pope Innocent II.