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. 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.