 During the medieval period , Britons regarded Constantine as a king of their own people , particularly associating him with Caernarfon in Gwynedd . While some of this is owed to his fame and his proclamation as Emperor in Britain , there was also confusion of his family with Magnus Maximus 's supposed wife Saint Elen and her son , another Constantine ( Welsh : <unk> ) . In the 12th century Henry of Huntingdon included a passage in his Historia Anglorum that the emperor Constantine 's mother was a Briton , making her the daughter of King Cole of Colchester . Geoffrey of Monmouth expanded this story in his highly fictionalized Historia Regum Britanniae , an account of the supposed Kings of Britain from their Trojan origins to the Anglo @-@ Saxon invasion . According to Geoffrey , Cole was King of the Britons when Constantius , here a senator , came to Britain . Afraid of the Romans , Cole submitted to Roman law so long as he retained his kingship . However , he died only a month later , and Constantius took the throne himself , marrying Cole 's daughter Helena . They had their son Constantine , who succeeded his father as King of Britain before becoming Roman Emperor . 
