The former French Catholic diocese of Alais (now written Alès, and in Latin: Alesiensis) was created in 1694, out of territory previously part of the diocese of Nîmes. It was suppressed after the French Revolution, with its territory being divided between the diocese of Avignon and the diocese of Mende. Its seat was Alès Cathedral.
About 570, Sigebert, King of Austrasia, created a see at Arisitum for a bishop named Monderic, taking fifteen parishes to create a territory for him. 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'). Archbishop Nicetius, who was the bishop of Lyon and Metropolitan of the diocese of Langres, intervened on his behalf and sheltered him in Lyon for two months. Unable to get his original place restored, Monderic fled to King Sigibert, who assigned him the 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. When Bishop Tetricus of Langres died, Gregory of Tours' kinsman Silvester was chosen to succeed him, and he proceeded to Lyon for consecration. The identification of Alais with 'Arisitum' was argued by Auguste Longnon, on very slender evidence. There are several other possibilities, as Louis Duchesne notes. The geography seems better suited to Neustrasia and to Aquitaine rather than to the lower parts of the Rhone valley.
A Bishop of Arisitum named Emmo is said to have participated in the Council of Clichy in 627, but neither the name Emmo nor the diocese Arisitum appear in the subscription list of that Council. His name does appear as a participant in a synod held at Reims, but only in Flodoard's Historia ecclesiae Remensis. This synod is not dated, and its acts quoted by Flodoard, do not appear in collections of church councils and synods. Louis Duchesne has noticed that the acts quoted by Flodoard are actually borrowed from the Council of Clichy in 627.