[1][2] Legend relates how a disciple of Jesus Christ, one Bonifatius, preached the Gospel in Cagliari in the 1st century.

There were probably bishops at Cagliari from an early date, however, as Athanasius of Alexandria speaks of previous episcopal martyrs (during the Diocletian persecution most likely) in a letter to his contemporary, the first well-known bishop of Cagliari, Lucifer.

In 1075, Pope Gregory VII reproached the Archbishop James for wearing a beard, a fashion which had been introduced into Sardinia at an earlier date; the pope asked the Judge Torchitorio I to oblige the clergy to abandon this custom.

The same bishop and his colleagues were blamed by Pope Victor III (1087) for neglect of their churches.

In the 12th century, however, the prominence of Cagliari was reduced vis-à-vis the Archdiocese of Torres in the north of the island.