Procopius relates that:

‘They imagine that the souls of the dead are transported to that island. On the coast of the continent there dwell under Frankish sovereignty, but hitherto exempt from all taxation, fishers and farmers, whose duty it is to ferry the souls over. This duty they take in turn. Those to whom it falls on any night, go to bed at dusk; at midnight they hear a knocking at their door, and muffled voices calling. Immediately they rise, go to the shore, and there see empty boats, not their own but strange ones, they go on board and seize the oars. When the boat is under way, they perceive that she is laden choke-full, with her gunwales hardly a finger’s breadth above water. Yet they see no one, and in an hour’s time they touch land, which one of their own craft would take a day and a night to do. Arrived at Brittia, the boat speedily unloads, and becomes so light that she only dips her keel in the wave. Neither on the voyage nor at landing do they see any one, but they hear a voice loudly asking each one his name and country. Women that have crossed give their husbands’ names.’

Source: Brittia – Wikipedia