Cnobheresburg was a castrum in East Anglia, where in about 630 the first Irish monastery in southern England was founded by Saint Fursey as part of the Hiberno-Scottish mission described by Bede.
Map of Chambersburg, PA, USA
The Venerable Bede, in his Ecclesiastical History of the English People, relates that Saint Ultan joined the mission led by Saint Fursey which went from Ireland through British territory to East Anglia around 633 AD, to the kingdom of King Sigeberht of East Anglia. The monastery at Cnobheresburg, of which he was a member, was established in the precinct of an old, stone-built, Roman shore-fort near the sea. The King received them and endowed the monastery, and it was later re-endowed by King Anna of East Anglia and his nobles.
Following the attack on the monastery in 651 by Penda of Mercia, Anna of East Anglia was forced by Penda to flee into exile.
The location is unknown. The site is commonly identified with Burgh Castle (Norfolk) near the mouth of the river Yare, thought to be the Garianonum of the Notitia Dignitatum and of the geographical description of Britain by Claudius Ptolemy.
Historians find many arguments against this location, but are unable to agree on a better one. The Roman fort at Burgh Castle was excavated by Charles Green during 1958-61. A detailed report by Norfolk Museums Service in 1983 (East Anglian Archaeology 20) shows that there was never any monastic settlement in Burgh Castle itself.