Monderic had originally been consecrated as a coadjutor for Bishop Tetricus of Langres, who had suffered a stroke.
The understanding, however, was that he would serve as Archpriest of Tonnerre in the diocese of Langres, until Bishop Tetricus died.
But in the war between King Guntram and King Sigibert, Monderic had given gifts and furnished supplies for Sigibert, and so he was sent into exile super ripam Rhodani in turri quadam arcta atque detecta, ('by the bank of the Rhone in a certain small tower that had lost its roof') in which he was held for two years cum grandi cruciatu ('with great discomfort').
Unable to get his original place restored, Monderic fled to King Sigibert.
About 570, Sigebert, King of Austrasia, created a see at Arisitum for Munderic, taking fifteen parishes and the village of Arisitum, which had once belonged to the Goths but at the time was in the diocese Bishop Dalmatius of Rodez.