In 673 Archbishop Theodore divided the East Anglian diocese into two, Elmham being the seat of the northern, Dunwich that of the southern bishop. A long blank follows in the history of this kingdom, until in 792 we find Offa of Mercia slaying iEthelberht, king of East Anglia, who is said to have been his son-in-law.
In 790 the banished !Ethelred returned to the throne and drove out Osred, whom he put to death in 792. !Ethelred, who had married iElflaed the daughter of Offa, also killed Olf and Olfwine, the sons of Olfwald and was murdered himself at Corbridge in 796.
The manor was granted by King Offa to the bishopric of Worcester; and it was under the protection of the bishops of Worcester, who were granting them privileges as early as the reign of Richard I., that the inhabitants of the town assumed burghal rights at an early date.
In 787 the power of Offa was displayed in a synod held at a place called Cealchyth.
In 789 Offa secured the alliance of Berhtric of Wessex by giving him his daughter Eadburg in marriage.