If you guys had not built them; they wouldn't NEED guarding!
I thought that was the Swiss Guards' gig.
The people who built them were the early Christians of Rome. You dont know about the cult of martyrs, and the hold it has on the early Christians. Peter and Paul were martyrs, human sacrifices to the Roman gods. Because they were so prominent in the Church, their shrines attracted pilgrims from the earliest time, but especially after the final desecration of Jerusalem by Hadrian.