Mortemer is a commune in the Seine-Maritime department in the Normandy region in northern France.

Mortemer is a small forestry and farming village situated in the valley of the river Eaulne in the Pays de Bray, some 23 miles (37 km) southeast of Dieppe at the junction of the D7, D36 and the D929 roads.

It was the site of the battle of Mortemer in February 1054 and was a defeat for Henry I of France when he led an army against his vassal, William the Bastard, Duke of Normandy in 1054.

The nature of the family's relations confused Robert of Torigni, one of the authors of the Gesta Normannorum Ducum.

But possibly Robert missed out a generation, as he did in dealing with the family history of the Montgomerys.