The siege of Paris of 885–886 was part of a Viking raid on the Seine, in the western part of the Frankish Empire. The siege was the most important event of the reign of Charles the Fat and a turning point in the fortunes of the Carolingian dynasty and the history of France. It also proved for the Franks the strategic importance of Paris at a time when it also was one of the largest cities in West Francia. The siege is the subject of an eyewitness account in the Latin poem Bella Parisiacae urbis of Abbo Cernuus.
With hundreds of ships, and possibly tens of thousands of men, the Vikings arrived outside Paris in late November 885, demanding tribute. This was denied by Odo, Count of Paris, despite the fact he could assemble only several hundred soldiers to defend the city. The Vikings attacked with a variety of siege engines but failed to break through the city walls despite days of intense attacks. The siege was maintained for months but without any significant assaults after the initial attack. As the siege continued, most of the Vikings left Paris to pillage further upriver. The Vikings made a final unsuccessful attempt to take the city during the summer. In October, Charles the Fat arrived with his army.