The Venerable Bede, in his "Ecclesiastical History of the English People", relates that Ultan joined the mission led by Fursa which went from Ireland through British territory to East Anglia in around 633 AD, to the kingdom of King Sigeberht of East Anglia. The monastery of which he was a member there was established in the precinct of an old Roman stone-built shore-fort near the sea, at a place called Cnobheresburg. The King received them and endowed the monastery, and it was later re-endowed by King Anna of East Anglia and his nobles. 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.