Berengar II (died 896) was the Count of Bayeux and Rennes and Margrave of the Northern or Norman March from 886 until his death a decade later.
The resulting surge of Viking attacks made possible by the power vacuum was narrowly held at bay by a hasty Breton-Frankish alliance between Alan the Great of Vannes and Berengar of Rennes.
Between 889 and 90, the Seine Vikings moved into Brittany, hard on the heels of the Loire fleet that Alan and Berengar had successfully driven out (this latter force had broken up into several small flotillas and sailed west).
Finding their retreat down the Marne blocked, the Vikings hauled their ships overland to the Vire and besieged Saint-Lo, where the Bretons virtually annihilated the fleet.
Berengar is speculated to have married the daughter of Gurvand, Duke of Brittany, by which relationship he attained the countship of Rennes.