 Among them was the so-called "Tomb of the Julii" with mosaics that appeared to be Christian.The burial chambers were uncovered again in 1939 as workmen dug a tomb for Pope Pius XI.Over the next ten years, Monsignor Ludwig Kaas oversaw an archaeological excavation of the pagan mausoleum complex under the foundations of St. Peter's Basilica (the Vatican Necropolis), dating to the 2nd and 3rd centuries.