Lambert was eventually killed in battle at Florennes, fighting against his old enemy Godfrey "the childless", the Duke of Lower Lotharingia who represented royal authority in the region.
Lambert was the son of Gilbert's nephew Reginar III who helped lead a French attempt to take over Lotharingia in 944,[1] and was exiled from the Holy Roman Empire in about 958 after being defeated in another Lotharingian rebellion.
[3] Among the sources which confirm this killing, the chronicle known as the deeds (Gesta) of the bishops of Cambrai adds that the new young German emperor Otto II, when he heard of this, gathered a force to besiege them, and then destroyed the castle, took them captive, and banished them from the country.
[4] The Gesta claims that Werner and Rainold had been assigned by Duke Bruno to govern Hainaut after the death of Count Richar, who had died the year before.
It also notes that after this defeat the brothers engaged in plundering and disturbances of the peace, and then withdrew to Carolingian-ruled northern France where they improved their military practices and gained the support of Charles, Duke of Lower Lorraine, a rebellious younger brother of the French King Lothair of France, who was one of the last ruling members of the Carolingian dynasty, and Eudes, the son of his ally and kinsman Adalbert I, Count of Vermandois.
This was reported in the early 11th century by Alpertus of Metz, who described Count Lambert as having been a desperado, a leader of bandits (praedones) who he preferred not to even name, and who profited from the blood and booty of the citizens, and then hid in forests and swamps.
In contrast, Alpertus praised Count Ansfried, who became bishop of Utrecht in 995, saying he had often defeated the bandits in Brabant, but without disadvantaging the citizens in the way Lambert did.
[12] The entry of Flanders into Lotharingia was a major turning point, balancing the power of the House of Ardenne, and giving Lambert and his family a new long-run ally.
Some time after 1010, Alpertus described Lambert as an ally (cliens) of Count Balderic, whose powerbase was around the area east of Nijmegen near the modern border of Germany and the Netherlands.
Lambert and Count Gerhard of Metz, described as Balderic's closest friend, were called upon to besiege a new fortification made on the banks of the Maas river, by his "Saxon" rival from north of the Rhine, Wichmann of Vreden [nl; de].
As the situation escalated Alpertus wrote that Gerhard and Lambert "said that they would endure travails and dangers" because "these two men were always prepared to stir up any kind of commotion or rebellion".
Modern historians see this battle as one step in a long-term push by Lambert and his descendants to take control of the region to the east of Leuven, the county of Brugeron, a part of the fertile Hesbaye, which was in the possession of the prince-bishopric of Liège.
Dietmar's report of his death described Lambert as the much hated son of Reginar, who was the worst person in his whole country, and had strangled many people in churches with bell ropes.
The historian Michel de Waha has argued that the family only gained full legitimacy in their father's county of Hainaut after this marriage.
As recounted by Dietmar, Wichmann of Vreden was killed in 1016, thus putting Balderic, who was suspected to be involved, at odds with Emperor Henry II.