Treaty of Saint-Clair-sur-Epte
The Treaty of Saint-Clair-sur-Epte was signed in the autumn of 911 between Charles the Simple (Charles III of France) and Rollo, the leader of the Vikings, which permitted the Normans to settle in Neustria in return for their protection of Charles' kingdom from any new invasion by the "northmen". No written records survive concerning the creation of the Duchy of Normandy.
In 911, a group of Vikings lead by Rollo attacked Paris before laying siege to Chartres. The appeals for help of the Bishop of Chartres, Joseaume, were answered by Robert, Marquis of Neustria, Richard, Duke of Burgundy and Manasses, Count of Dijon. On 20 July 911, at the Battle of Chartres, they defeated Rollo despite the absence of many French barons and also the absence of the French King Charles the Simple.[1] After the Frank victory near Chartres on 26 August, Charles decided to negotiate with Rollo. The talks, led by Hervé, the Archbishop of Reims, resulted in the Treaty of Saint-Clair-sur-Epte. The treaty granted Rollo and his soldiers all land between the river Epte and the sea "in freehold and good money." In addition, it also granted him Brittany "for his livelihood". At the time, Brittany was an independent country which France unsuccessfully had tried to conquer. In exchange, Rollo guaranteed the king his loyalty, which involved military assistance for the protection of the kingdom. As a token of his good will, Rollo also agreed to be baptised and marry Gisela, a presumed illegitimate daughter of Charles.[2]
The territory covered by the treaty corresponds to the northern part of today’s Upper Normandy down to the Seine, but would eventually extend west beyond the Seine to form the Duchy of Normandy, named so because of the Norsemen which ruled it.
The treaty was entered into after the death of Alan I, King of Brittany and while another group of Vikings occupied Brittany. Around 937 Alan I's son, Alan II returned from England to expel those Vikings from Brittany in a war that was concluded in 939. During this period the Cotentin Peninsula was lost by Brittany and gained by Normandy.