Inside the Basilica and its underground chambers you can observe the layering of the levels and relive the civilizations that developed in Rome throughout the centuries.
The upper level houses a medieval basilica constructed with spoils, such as columns, and decorated with stunning mosaics. Moreover, the Cosmatesque-style paving is one of the most impressive in the city.
During the 15th century, Pope Martin V commissioned the construction of a chapel to consecrate to Saint Catherine of Alexandria. It was then decorated by Masolino da Panicale, probably with the assistance of his pupil Masaccio.
The main furnishings, such as the tabernacle, date from the construction of the Basilica (12th c.). However, some elements come from the church located ten metres below and discovered in 1858 by Prior Mullooly. It is a primitive basilica dating from the 4th century, built by Constantine I, which still preserves one of the most ancient inscriptions in vernacular.
A fresco was discovered on one of the walls, depicting the story of an announced tragedy that turned into a miracle. Upset about the conversion of his wife to Christianity, the prefect Sisinnio accused Saint Clement of being responsible for this and ordered his arrest. When Sisinnio sent his slaves to abduct Clement, they made a mistake and brought back a column instead.
Located on another level inside the Basilica are the remains of a Roman house dating from the 1st century BC. Inside you can see a 2nd-century mithraeum, a temple where the god Mithras was worshipped. Along two sides of the room are the typical benches and a replica of the altar with a relief depicting Mithras killing the bull stands in the centre.
The mithraeum is an absolutely striking room worth visiting to contemplate the architectural and urban evolution of Rome, as well as its cultural and religious transformation.