Located at the confluence of the Sar and Ulla rivers, Iria was a port city, the main seat of the Celtic Capori tribe, on the road between Braga and Astorga.
King Juan Carlos of Spain granted the illustrious resident and writer Camilo José Cela the title of Marqués de Iria Flavia.
To restore Catholic orthodoxy in the Visigothic marches that were recovered from the Kingdom of the Suebi (Galicia) in a series of campaigns during the years leading up to 585, nine dioceses were established in Galicia, including Iria Flavia, mentioned in the document Parroquial suevo (ca 572–582); the Parroquial divides the region into dioceses and marks the first definitive integration of this zone in the monarchy of the Visigoths, who had been catholicized from Arianism in 587 (Quiroga and Lovell 1999).
No commercial or political rationale for siting a bishop at Iria Flavia seems to present itself, though excavations have identified a cult sanctuary dating to the second half of the sixth century (Quiroga and Lovelle 1999).
In 1095, through reverence for the body and the sepulchre of St James, Urban II, by a Bull of December 5, withdrew from Iria its episcopal rank and transferred the see in its entirety to Compostela, in favour of the Cluniac bishop, Dalmatius, present at the Council of Clermont that year.