[1] The diocese dates back to 948, when Adam of Bremen noted that Reginbrand, bishop of Aarhus, attended the synod of Ingelheim in Germany.

The last Catholic bishop, Ove Bille resisted the Reformation, aided by Poul Helgesen, prior of the Carmelite monastery at Elsinore.

The St. Clement Chapel may have been the first Christian structure to be built centrally in Aarhus, within the walls and on the former pagan burial site.

In c. 1180 Niels of Aarhus, illegitimate son of King Canute V of Denmark, died and was buried in the St. Clement Chapel.

Niels' death was followed by stories of supernatural events and healing powers at his grave, followed by significant offerings and worship at his tomb.

In 1191 the king appointed Peder Vognsen as the new bishop of Aarhus and he quickly moved to stop the unauthorized worship.