The only certain fact is that, at the time of San Frediano in the 6th century, there was already a church in that position, which had replaced the primitive cathedral of Santa Reparata when it was no longer able to contain all the population. In the 8th century a crypt was added for the body of San Regolo, which had been transferred from Populonia. The Duomo was completely rebuilt between 1060 and 1070, with five naves, re-using materials as ancient columns and capitals.However, little remains even of this phase of the church. The cathedral acquired its present appearance after interventions in the 12th century, which finished in 1204, adding the portico to the façade, with three large arches and the "loggias" with multiform columns, while the pediment, although planned, was never realised.