The Romanesque Abbey church was constructed in the mid-11th century and contains many beautiful 11th- and 12th-century murals which are still in a remarkable state of preservation. It has been a UNESCO World Heritage Site since 1983.
The cruciform church carries a square tower over its crossing. The transept was built first, then the choir with its ambulatory with five radial chapels in the polygonal apse. In the next building campaign, three bays of the nave were added, the bell tower and its porch, and finally the last six bays of the nave. The bell tower is finished by a fine stone spire more than 80 meters high, added in the 14th century (and restored in the 19th century).
The barrel vaulted nave is supported on magnificently-scaled column with foliate capitals.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.