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.

[1] 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.

After being welcomed by Erchinoald at Péronne and by Clovis II and Queen Balthild, Fursey was granted an estate at Lagny on the Marne, where he built a monastery.

Foillan and Ultan took away the precious property and books of the monastery, and after unhappy dealings with Erchinoald they were received by Ste Gertrude of Nivelles and her mother Itta.

These two Irish monks complied with her request, and built an adjoining monastery at Fosse, in the diocese of Liege.