Brittany in the 9th century
The Duchy of Brittany that emerged in the early 10th century was influenced by several earlier polities. Prior to the expansion of the Roman Empire into the region, Gallic tribes had occupied the Armorican peninsula, dividing it into five regions that then formed the basis for the Roman administration of the area, and which survived into the period of the Duchy. These Gallic tribes – termed the Armorici in Latin – had close relationships with the Britonnes tribes in Roman Britain. Between the late 4th and the early 7th centuries, many of these Britonnes migrated to the Armorican peninsula, blending with the local people to form the later Britons, who eventually became the Bretons. The reasons for these migrations remain uncertain.[d] These migrations from Britain contributed to Brittany's name.
Brittany fragmented into small, warring regna, kingdoms, each competing for resources. The Frankish Carolingian Empire conquered the region during the 8th century, starting around 748 taking the whole of Brittany by 799. The Carolingians tried to create a unitary administration around the centres of Rennes, Nantes, and Vannes using the local rulers, but the kings of Brittany's hold on the region remained tenuous. Carolingian technology and culture began to influence Brittany, and the church in Brittany also began to emulate the Frankish model.
The greatest influence on the later Duchy, however, was the formation of a unitary Brittany kingdom in the 9th century. In 831 Louis the Pious appointed Nominoe, the Count of Vannes, ruler of the Bretons, imperial missus, at Ingelheim in 831. After the death of Louis in 840, Nominoe rose to challenge the new emperor, Charles the Bald, emboldened in part by new Viking raids on the empire. Charles the Bald created the Marches of Neustria to defend Western Francia from the Bretons and the Vikings. Erispoe fought Charles the Bald, who felt that a quick attack would successfully challenge the new Breton leader. Erispoe won a victory at the Battle of Jengland and, under their Treaty of Angers in 851, Brittany's independence was secured.
The new kingdom proved fragile and collapsed under Viking attack. In 853 the Viking Godfried left the Seine with his fleet, sailed around the Breton peninsula and sacked Nantes. Erispoe entered into an alliance with the leader of another Viking fleet, Sidroc, who betrayed him, resulting in Erispoe's defeat at the hands of the Vikings. A weakened Erispoe ruled until 857 when he was assassinated and then followed as Breton ruler by his cousin and rival, Salomon, the Count of Rennes and Nantes. Viking raids continued. Alan I successfully defeated one wave of Vikings around 900, expanding the kingdom to include not only the Breton territories of Léon, Domnonée, Cornouaille, and the Vannetais, but also the Frankish counties of Rennes, Nantes, Coutances, and Avranches, as well as the western parts of Poitou and Anjou. Alan I's military success resulted in a period of peace from Viking invasions and few raids from the Vikings were recorded from 900 through to 907.
After Alan I's death in 907, Brittany was overrun once again by Vikings. Fulk the Red, Count of Anjou, is said to have occupied Nantes from 907 to 919 when he abandoned it to the invading Vikings. In 919, the great Viking fleet of Rognvaldr landed in Nantes, quickly coming to dominate the region. This invasion accelerated the exodus of Bretons, including that of the
machtierns, "the local hereditary officers upon whom the civil administration depended". Among the refugees were Mathedoi, the Count of Poher, and his son Alan Barbetorte, the grandson of Alan I; they fled to England and lived in exile in the courts of Edward the Elder and Edward's son and successor Æthelstan. The Viking occupation of Brittany lasted until about 936. Little recorded history of this period is available until Alan Barbetorte returned in 937 to expel the Vikings and reestablish a version of the former Carolingian kingdom.