The grave of the pope - immovable?

Pope Benedict V was set down and banished from Rome to Hamburg in 964, where he died a year later. Decades later, his mortal remains were transferred to Rome. In 1300 a tomb was donated in Hamburg's St. Mary's Cathedral to the memory of Benedict V, which was removed in 1780. Various fragments were found in excavations. Benedict's tomb is regarded as proof of the location of St. Mary's Cathedral. Since at least the 10th century it has stood at the same place as it does today.