The basilica of Santa Maria in Trastevere is one of the oldest churches in Rome, perhaps the first in which mass was openly celebrated. The basic floor plan and wall structure of the church date back to the 340s AD.
This is the queen of the churches in Trastevere. The inscription on the episcopal chair says that it is the first church dedicated to the Mother of God, although actually that privilege belongs to Basilica di Santa Maria Maggiore. In its foundation it is certainly one of the oldest churches in the city.