▁in ▁his ▁mission , ▁and , ▁having ▁made ▁a ▁very ▁favor able ▁impression ▁at ▁the ▁Norman ▁court , ▁spent ▁some ▁years ▁in ▁that ▁country . ▁During ▁a ▁second ▁stay ▁in ▁Norm andy , ▁D udo ▁wrote ▁his ▁history ▁of ▁the ▁Norm ans , ▁a ▁task ▁which ▁Duke ▁Richard ▁had ▁ur ged ▁him ▁to ▁undert ake . ▁Very ▁little ▁else ▁is ▁known ▁about ▁his ▁life , ▁except ▁that ▁he ▁died ▁before ▁ 1 0 4 3 . ▁ ▁Historia ▁Norm ann orum ▁ ▁Writ ten ▁between ▁ 9 9 6 ▁and ▁ 1 0 1 5 , ▁his ▁Historia ▁Norm ann orum — also ▁known ▁as ▁Lib ri ▁III ▁de ▁mor ibus ▁et ▁act is ▁prim orum ▁Norm ann iae ▁duc um ▁and ▁G esta ▁Norm ann orum — was ▁dedicated ▁to ▁Ad al ber on , ▁bishop ▁of ▁La on . ▁D udo ▁does ▁not ▁appear ▁to ▁have ▁consult ed ▁any ▁existing ▁documents ▁for ▁his ▁history , ▁but ▁to ▁have ▁obtained ▁his ▁information ▁from ▁or al ▁tradition , ▁much ▁of ▁it ▁being ▁supplied ▁by ▁Ra oul , ▁count ▁of ▁I v ry , ▁a ▁half - bro ther ▁of ▁Duke ▁Richard . ▁Con sequently , ▁the ▁Historia ▁part akes ▁of ▁the ▁nature ▁of ▁a ▁rom ance , ▁and ▁on ▁this ▁ground ▁has ▁been ▁regarded ▁as ▁un tr ust worth y ▁by ▁such ▁compet ent ▁critics ▁as ▁Ernst ▁D ü m ml er ▁and ▁Georg ▁Wait z . ▁Other ▁authorities , ▁such ▁as ▁Jules ▁La ir ▁and ▁Johannes ▁Ste en stru p , ▁while