The Bretons, led by King Salomon, began to occupy the west coast of the Cotentin Peninsula from 836. Before their advances, in August 867, Charles the Bald gave Salomon the Comitatus Constantiensis, territory over which he had little influence. In 889, the Vikings travelled up the Vire and besieged Saint-Lô. Protected by solid ramparts built, according to tradition, in the early 9th century by Charlemagne, the town did not initially surrender. The attackers then cut the water supply, resulting in the surrender of the inhabitants. The Vikings massacred the inhabitants, including the Bishop of Coutances, and then razed the town. The seat of the diocese moved to Rouen. It was only in 1025 that Bishop Herbert decided to return to the walls of Saint-Lô and restore the episcopal see. Then, under Geoffrey de Montbray, the town had a great economic development, taking advantage of the Norman expedition in Sicily. Robert Guiscard, a close associate of Geoffrey, brought important loot to Apulia and Calabria, and it was thanks to this treasure that Geoffrey was able to rebuild Coutances Cathedral in 1056. Saint-Lô is famous for its goldsmiths and even Matilda of Flanders, the wife of William the Conqueror, ordered two candelabra for the .