You will be surprised by the answer. I certainly was. And I agree with the scholar’s choice.
CNA reports: Do we know when the first church building was constructed and where it was located? If not, what is the oldest known church building that has survived — if not intact, then at least in ruins?
You ask a question about Christian Archeology, a very important topic because of the Catholic’s Church claim of apostolic origin. We can trace the Catholic Church back to the time of Christ by means of the unbroken succession of Roman pontiffs. In fact, we know exactly where St. Peter was buried. Read the answer here.