The Siege of Chartres took place in spring 911 during the age of Viking incursions in Europe. The Viking leader, Rollo, and his men laid siege to the city of Chartres, in West Francia. But they failed to achieve their goal before the arrival, in July 911, of a relief army sent to battle them. The engagement that ensued resulted in the defeat of the Norsemen. Although, Viking raids were far from being a rare occurrence as the Frankish realms had to contend with such sudden incursions for decades, this one would prove to have everlasting consequences on European history.

Rollo was a Viking who, as Count of Rouen, became the first ruler of Normandy, a region in today's northern France. He emerged as a leading warrior figure among the Norsemen who had secured a permanent foothold on Frankish soil in the valley of the lower Seine after the Siege of Chartres in 911. Charles the Simple, king of West Francia, granted them lands between the mouth of the Seine and what is now Rouen in exchange for Rollo agreeing to end his brigandage, swearing allegiance to him, religious conversion and a pledge to defend the Seine's estuary from other Viking raiders.