Dommoc (or Domnoc), a place not certainly identified but probably within the modern county of Suffolk, was the original seat of the Anglo-Saxon bishops of the Kingdom of East Anglia. It was established by Sigeberht of East Anglia for Saint Felix in . It remained the bishopric of all East Anglia until , when Theodore of Tarsus, Archbishop of Canterbury, divided the see and created a second bishopric at either North Elmham, Norfolk, or South Elmham, Suffolk. The see of Dommoc continued to exist until the time of the Viking Wars of the 860s, after which it lapsed.
Foundation
The primary authority for the foundation of the see of Dommoc is Bede's Historia ecclesiastica which stipulates Felix's mission in relation to Sigeberht's rule. Following the assassination of Eorpwald of East Anglia by Ricberht in the kingdom fell back into "error" for three years, before Sigeberht, brother or half-brother of Eorpwald, took possession of the kingdom. Sigeberht had lived in exile in Gaul during his brother's lifetime, where he had been initiated in the sacraments of the Christian faith, becoming a very Christian man of learning. On his accession he resolved to ensure that the whole kingdom shared his faith and he was very ably supported by Saint Felix. Felix had been born and consecrated in Burgundy. He came to Archbishop Honorius of Canterbury (Saint Honorius) and expressed his desire to preach the Gospel of Life. Honorius sent him to the East Angles, where he found a fruitful multitude of believers and brought that whole province to the faith and works of righteousness. He accepted the episcopal seat in the city ('') of Dommoc, and when he had governed it for seventeen years he died there in peace. An alternative account surviving in the much later work of William of Malmesbury relates that Sigeberht and Felix came to the kingdom together from Gaul.
Early chronology
The date of the foundation of Dommoc is estimated from the foregoing events and from the duration of tenure of the first three bishops. Edwin of Northumbria was baptised by Paulinus of York at Easter 626 and they then undertook the conversion of the Kingdom of Lindsey and of Eorpwald and his kingdom. Eorpwald was slain soon after his baptism, after which there was a reversal of faith for three years. Felix was bishop for seventeen years, his successor Thomas for five, and his successor Berhtgisl Boniface for a further seventeen (a total of 39 episcopal years). Both Thomas and Berhtgisl were consecrated by Archbishop Honorius, who died in 653. After Berhtgisl's death Archbishop Theodore, who reached Canterbury in 668–689, appointed Bisi to Dommoc, and Bisi attended the Council of Hertford in 673. By then Bisi's health was declining so that he was unable to administer the diocese and soon afterwards Theodore divided the see. Since Berhtgisl cannot have died later than 670, the foundation of Dommoc should date to and the assassination of Eorpwald to . This would place the death of Felix at and of Thomas . That would accord with the tradition that Felix baptised Saint Æthelthryth (Etheldreda) in or soon after 631 at Exning and with William of Malmesbury's statement that he baptised Cenwalh of Wessex in East Anglia before that king was restored to Wessex by King Anna in .
Location
Despite its former importance, the original location of Dommoc has been lost for many centuries and forms the subject of scholarly debate. This reflects rival claims staked during the 13th century by the monks of Eye, Suffolk (for Dunwich, Suffolk), and of Rochester in Kent (for Walton, Suffolk). The uncertainty therefore arose between the tenth and twelfth centuries. William Camden, in his Britannia, promoted general acceptance of the identification with Dunwich, formerly a splendid city on the Suffolk coast between Aldeburgh and Southwold, all but a tiny part of which has now been lost to coastal erosion. The Rochester claim for Walton refers to the place near or in Felixstowe, Suffolk, at the tip of the Colneis Hundred peninsula between the River Deben and the River Orwell. This Walton is not to be confused with Walton-on-the-Naze, Essex, which stands on the south side of the Orwell and Stour estuary mouth, and which has never been seriously considered as a candidate for Dommoc. The scholarly revival of the claim for Walton as Dommoc was the work of Stuart Rigold.