Here is a description of the Church of St. Clement in Rome. What is not said here is that the lower 4th century church was discovered in the 19th during excavation for city improvements. until that time the existing church was thought to be the 4th century structure, because the mosaic in the apse dates from that period. [The travelogue gives 12th century for this mosaic. I repeat here what I had read previously.]When the older church became unusable, it was filled in with rubble, the movable art work having been removed, and an exact replica was built on top. The Pastor of the church at this time reasoned that there might be yet another structure farther down. Having received funds for the purpose, the Father excavated and found the two structure mentioned in the account linked above. However the Church authorities believed then and at least until the 1960's that the Roman house was in fact a House Chapel dedicated to St. Clement, dating from apostolic times. This account I produce from memory, from a pamphlet that came from the Church of St. Clement. I no longer have the book, but I think my recollection is accurate.
St. Clement was revered as a Saint from earliest times. Indeed the Church Fathers thought seriously of including his epistles in the New Testament.