Little is known about William Longsword’s birth and upbringing, though unlike his father, who was always known by the Northmannic name Rollo even after his ‘baptism’ in 912 under the name Robert, William is known only by a Frankish name. Although he was born before the agreement with Charles the Simple in 911, Rollo had either been Frankified sufficiently or was perhaps being politically acute to give his son a Frankish name. There are no contemporary records stating when William was born although the Heimskringla, the saga of Saint Olaf written in the twelfth century, states that he was born in 905 or 906 in Rouen. This differs from both Dudo of St Quentin and the Planctus which both state that William was born ‘overseas’.
Rollo was still living in 928, when he was holding Eudes, son of Herbert of Vermandois, as a captive according to Flodoard, and was probably dead by 933, when his son William was mentioned as leading the Normans by Flodoard. Rollo progressively transferred power to William from as early as 927 and from 928-9 he can be considered as the new leader of the Rollonids. His succession was confirmed by him publicly taking the sword of his father in the cathedral at Rouen. This reinforced his position as a Christian ruler since the Church was seen in take part in the appointment of a new leader through their participation in this communal activity.
Between 911 and 931, the Rollonid Normans had played no direct role in Brittany. This has been occupied by the Norman settlements on the River Loire and Rollo maintained close contact with them just as he did with the rest of the Scandinavian world. The Cotentin and Avranchin had been under the theoretical control of the Breton counts of Rennes and Dol since 874. However, after the treaty in 924 between Rollo and Ralph, king of France, the Bessin, Hiesmois and the Seois were accepted as part of the Rollonid sphere of influence and in 927 the counts of Rennes and Dol had little choice but to accept the sovereignty of the Rollonids over the Cotentin and Avranchin. It is also possible that the counts performed homage to Rollo or gave an oath of non-aggression with respect to his borders.
In 930, the Loire Normans attacked the Saintonge, Angoumois, Perigord and Limousin. The French king defeated them at Estresse, near Beaulieu in the Correze and their depleted force returned to their base near Nantes. This weakened the Norman settlements and the Bretons rose up in revolt killing Flekan, one of their chiefs. William Longsword had maintained close contacts with Inkon, the leader of the Loire settlements and supported him against the Breton rebels. The Breton counts of Rennes and Dol, despite their recognition of Rollonid sovereignty over the Cotentin and Avranchin, believed that they could benefit from William Longsword’s youth and inexperience and joined the revolt. They were initially defeated by William who then returned to Rouen but regrouped and invaded Rollonid territories as far as Bayeux. Defeated a second time, the count of Dol accepted the sovereignty of the Normans over Dol and Saint-Brieuc. By the end of 931, Brittany has been subdued from the east by the Rollonids and from the west by the Loire Normans. The Breton leaders were exiled.
By early 932, the Rollonids had progressively occupied the Cotentin, Avranchin and the territories of Dol and Saint-Brieuc. The Cotentin already had stable Scandinavian colonies but they were initially unwilling to accept William’s authority. It was important for William to establish his authority over this area because the Loire Vikings, vulnerable to Breton attack around Nantes, saw the Avranchin as a safer area for colonisation. The only other mention of William’s reign before his participation in the Frankish civil wars near the end of his life is Flodoard’s entry on his meeting with King Ralph in 933 at St Quentin, when William committed himself to Ralph and in return received ‘the land of the Bretons on the coast’. This confirmed that William Longsword had his protectorate over Brittany and possession of the Cotentin and Avranchin. Coinage minted during the rule of William Longsword bore the title ‘duke of Brittany’. By 933, the Rollonids had been given royal approval for their activities in what would later become Normandy. It does not, however, mean that they controlled all this territory, and in fact it would only be in the eleventh century that all Normandy fell under the power of the Rollonids. For example, it was not until 1030 that the bishops of Avranches felt safe returning to their see from Rouen, where they had lived in exile since the Northmannic incursions.
The conquest of these areas took time. The Vikings who occupied the Cotentin and Avranchin, like those of Bessin, remained ‘Scandinavian’ in character: they were pagan and highly independent. It proved difficult to get them to accept the authority of the Rollonid ruler, convert to Christianity and abandon their ‘Scandinavian’ ways. The southern areas of the Cotentin and Avranchin proved the most difficult to pacify and the Bretons in the extreme south of Brittany remained undefeated in 942. To prevent Breton attacks, William constructed fortifications at Pontorson to protect the crossing over the River Couesnon, refortified Avranches (where there was already a Carolingian castrum) and built a castle at Mortain. He also encouraged Scandinavian settlement of the eastern part of Brittany from the Viking colonies in the Cotentin, Britain and Ireland.
The significance of the expansion of the Rollonid territories lay in their increasing dominance (albeit tenuous on occasions as the revolt by Riulf in 934-5 shows) over other independent Scandinavian colonies. William had supported and arguably saved the Nantes settlements from destruction between 930 and 932 and the Contentin and Avranchin settlements had also been brought under his nominal sovereignty, though they were still not entirely secure at the end of his reign. The process of amalgamating separate independent Viking settlements under the control of the Rollonids that Dudo noted later in his chronicle had begun. Normandy, as it was to emerge in the eleventh century, was beginning to be established.
Dudo is the only source for the revolt of 934-5. Though his account should be viewed with considerable scepticism, it can probably be trusted, at least in its broad outline. The revolt is significant in several respects. It shows that Rollonid control over the Cotentin and Avranchin was far from secure and one of Riulf’s goals was the deposition of William Longsword because he had become too authoritarian in his attitude to other Viking groups. Secondly, and perhaps more importantly, it represented a clash between two different Viking approaches to colonisation. The Cotentin, Avranchin and Bessin retained their adherence to Scandinavian customs and pagan religion. By contrast, the Rollonids were seen as becoming too Frankish in their tastes. Riulf maintained that William Longsword intended to enrich his own relatives (Riulf may have heard that William intended to marry the daughter of the count of Vermandois) and his Frankish friends at the expense of other Vikings and denounced his contacts with the French king.
Riulf was called ‘count of the Cotentin’ by some later chroniclers though it is unclear whether he was the Viking leader or was acting on his behalf. There is also evidence that the revolt was encouraged by the Bretons and the Flemish count Arnulf, both of whom were threatened by the expansion of the Rollonids. Riulf sought independence for the lands situated to the west of the River Risle (Cotentin, Avranchin and Bessin) and according to Dudo sent an envoy to William demanding ‘all the land up to the Risle.’ William replied that he could not give Riulf the land but he did not say why, but offered to make Riulf in effect co-ruler, subordinate in name only. Riulf responded by moving an army towards Rouen, successfully crossing the Seine and camping outside the city in 935. Rouen was poorly defended and William is prepared to abandon it. Further negotiations occurred and William then offered Riulf the land ‘not only up to the Risle, but all the way to the Seine.’ Riulf, sensing weakness, again refused his offer.
William again contemplated flight to Francia, but is persuaded by his advisers into combat. Later chroniclers specifically mention the role played by Bernard the Dane, probably a leader from Roumois and the ‘old’ Bot, who is anachronistically called the ‘constable’ but who was probably either the leader of William’s bodyguard or his adviser on military matters. In what seems to have been a surprise attack, William fell on Riulf’s camp, scattering the rebel troops, killing many of them, and driving the rest (including Riulf himself) into flight. The Viking army is in no position to continue the revolt and Riulf disappears from the historical record.
As a partisan of the Rollonids, it is important to understand why Dudo told a story that reflected badly on one of his heroes. William here was portrayed as rather cowardly (or, taking a more positive position rather shrewd given his weak political and military position), making accommodations with Riulf at every opportunity, being persuaded to fight because of pressure from his advisers, and achieving victory through what appeared not to be the manliest of strategies. If this account was known widely enough in Rouen in the late tenth century, Dudo could not simply ignore it. This makes sense since Rouen prospered greatly through the Rollonid accommodation of both native Franks and immigrant Northmen, and if the city had been taken by hardcore, anti-Frankish Northmen, that prosperity would have been threatened. Dudo used the revolt to show what William was really made of. It shows, however, that twenty years after the official establishment of the Rollonid principality, control even over the capital city was insecure, and other Northmannic leaders of equal power were nearby, waiting for the chance to overthrow the Frankish-Northmannic regime of the Rollonids.
In 931, Aethelstan, king of Wessex had welcomed the main Breton exiles, notable Mathedoe and his son Alan ‘Red Beard’ to his court. There were also exiles from the Rollonids and the Vikings of the Loire in Flanders and France and who wished to free their lands. In 936, Aethelstan put a fleet of ships at Alan’s disposal and, with his supporters he landed on the coast of Brittany near Dol, surprised and massacred its Norman garrison before moving to the west. Despite the resistance of the Scandinavian colonists, he moved his increasingly large army and besieged Nantes. Count Even, one of his supporters also had considerable success against the colonists. On 1st August 939, the joint armies of Alan ‘Red Beard’, count Berenger and count Hugh II of Maine defeated the colonists at the battle of Trans, ten kilometres south-west of Pontorson. This freed Brittany from Norman occupation and Alan was proclaimed duke.
Significantly, Alan did not seek to reclaim the Cotentin or Avranchin where there were strong Norman garrisons unlike in Brittany and in 942, when he made homage of Louis IV of Francia he also solemnly renounced future claims over these areas. He also renounced Breton claims to Mayenne, perhaps as the price of support from Hugh II of Maine in 939. In 942, Harald ‘Bluetooth’, king of Denmark who had temporarily lost his throne obtained William Longsword’s agreement (in the name of Scandinavian solidarity) to settle in the Cotentin with his sixty ships until he was able to regain his throne. His presence, even temporarily reinforced the defences of western Normandy. In addition, during the 940s, a chain of castles was constructed from Tinchebrai to Teilleul to protect against attacks from Brittany. The Breton rebellion and the restoration of independent Breton rule effectively defined the western edge of Norman rule.
 The only study of William Longsword is the very dated Jules Lair, Étude sur la vie et la mort de Guillaume Longue-épée, duc de Normandie, Paris: Picard, 1893. Pierre Bouet ‘Dudon de Saint-Quentin et le martyre de Guillaume Longue Épée’, Pierre Bouet and François Neveux (eds.) Les Saints dans la Normandie mediévale, Caen, 2000, pages 237-258 is an important recent study.