 When the site underneath the church was excavated in the years 1965-66, an investigation revealed that the earliest building dates from the first century, and was 76 meters long and 71.5 meters wide.The inner room was 55.7 by 43.8 meters large, and held a mysterious shallow area used to store water, measuring 34 x 17.2 meters.This is notable because no similar structures from this period, North of the Alps have yet been found.