In northern Brittany an important geomorphological response to Holocene sea-level rise has been the development of coastal dunes with associated lagoons and marshes. At Anse du Verger, a marsh has formed behind a dune system which has been developing in situ for the last 4000 year. The lithostratigraphy of the marsh comprises extensive peat formation, with sands, silts and occasional sand lenses, the latter probably associated with storm surges. The sequence dates from 10,320+/-120 BP. After 3000 BP, flood episodes on the marsh are more common, while the upper marsh deposits can be correlated with the recent period of dune building. Prehistoric artifacts (remains of cooking implements) have been found on a cliff to the east of the marsh and are buried by washover deposits, which indicates a sudden abandonment of a settlement possibility due to a storm surge soon after 2460+/-80 BP. Surge levels are proposed as a controlling factor on dune crest elevation.