Coastal distributions such as that of the Neolithic chambered tombs of Brittany raise important questions about prehistoric beliefs and understandings relating to sea and shoreline. Concepts of liminality come particularly to the fore where headlands and islands are selected as places for the disposal of human remains. The density of chambered tombs recorded by Du Châtellier on the islands of the Molène archipelago, with its rocks, inlets and small islands exposed and covered by the tides, provides a prominent example of this coastal emphasis. The analysis presented here includes assessment of the reliability of the Du Châtellier inventory and of the topographic changes resulting from sea-level rise. It is argued that the dramatic transformative effect of the tides on the shallow waters of this archipelago will have enhanced the liminality of the setting and may have endowed the islands with special mythological or symbolic associations that may explain the density of the monuments. Ethnographic accounts of coastal beliefs from North America and northern Europe provide additional indications of the likely symbolic importance of such shoreline settings for Breton Neolithic communities.