Ancient Diocese of Saint-Malo

The former Breton and French Catholic Diocese of Saint-Malo (Latin: Dioecesis Alethensis, then Dioecesis Macloviensis) existed from at least the 7th century until the French Revolution. Its seat was at Aleth until the 12th century, when it was moved to Saint-Malo. Its territory extended over some of the modern departments of Ille-et-Vilaine, Côtes-d'Armor, and Morbihan. Until the 860s, it was sometimes termed the bishopric in (the monastery of) Poutrocoet.

In early Brittany, church organization was not centered on cities and dioceses, since the Roman system of government had not reached so far to the west and north, but on monasteries, populated from the British isles and Ireland. Dol, Treguier, and Alet were considered monastery-bishoprics until the 11th century.

Already by the mid-6th century the metropolitan bishop of Tours was struggling to exert his authority over the bishops of Brittany. At the Council of Tours in 567, which was attended by no bishop of Brittany, a canon forbade the consecration of any bishop of Armorica without the consent of the metropolitan.

In 826, after two generations of warfare between Franks and Britons, Brittany was conquered, and created a duchy by the Franks. Louis the Pious made the Breton Nominoe the first duke. But when the Emperor Louis died in 840, Nominoe embarked on an independence campaign for Brittany, while posing as a loyal adherent of the distant Emperor Lothair. His plan included ridding himself of bishops who had supported the Gallicising of the Breton church. Simony was a convenient charge.

Bishop Rethwalatrus is referred to as Redhuualatro episcopo in Poutrocoet in a document of 863, in the cartulary of Redon, and again in 858.

Incursions of the Normans into Brittany began in 843 with the sack of Nantes, repeated in 853 and 866. Treguier and Dol and the whole north coast were ravaged between 878 and 882. The abbey of Landévennec was destroyed in 913. In 919, there was general devastation throughout Brittany, causing nobles and monks, with their treasures, to flee the country. The abbey of Redon was destroyed. By 936, the Normans were masters of all Brittany.

In 965, Bishop Salvator, along with Abbot Juanus of Saint-Malo, was forced to flee to Paris from the Normans. He died there, perhaps around 1000.

At a synod held by Pope Leo IX in Reims in October 1049, several clergy of Tours laid a complaint through the archbishop of Reims before the assembly. The bishop of Dol and seven of his suffragans had attempted to secede from the metropolitanate of Tours, and form their own ecclesiastical province, with the bishop of Dol as archbishop and metropolitan, all without papal authority and contrary to custom. Pope Leo ordered the bishop to appear next year at the Roman synod to answer the charges. On 1 September 1050, he wrote to the duke and count of Brittany, informing them that, in accordance with previous papal decisions, all their bishops were subject to the archbishop of Tours, and that in no way could he approve the demand for a separate ecclesiastical province. He had excommunicated all the bishops, not only for their presumption, and their failure to appear at the Roman synod, but for their involvement in simony as well. They were not to carry out ecclesiastical functions or impart blessings.