Sometime around 530, two boats, both at the mercy of the seas and without human control, were voyaging around the North Atlantic and North Sea. One carried St Brendan and his companions, on their quest for the Land of Promise but passing from Ireland towards the Faroes on the way. Their boat was equipped with oars and a sail, but every so often, at Brendan’s urging, they set them aside and let God take them wherever He willed. The other boat contained a single woman, Constance, Chaucer’s Custance, the daughter of a Roman emperor named Constantine, who had been set adrift from Asia Minor and would finally come ashore in Northumberland; later, she would reverse the voyage to return to Rome, this time accompanied by her baby son Maurice, who would in due course become emperor himself. Without any means of steering, she was entirely in God’s hands, and was reliant on miracle alone to preserve her. The two stories invite combining in a meeting far out on the high seas: what might the saint have thought of the lone woman, or she of the small community of monks who formed Brendan’s crew? Might they have exchanged words, or prayers, or food and water, or their stories? And how might the stories themselves engage with each other?

It did not, of course, happen, and not just because Brendan actually existed, and Constance, in so far as she did exist, had a very different biography from the one the story records; nor because a voyage to the Faroes would pass well north of any destination in Northumberland – though that is more likely than that a boat set adrift in the eastern Mediterranean would reach the North Sea. Brendan was markedly long-lived (484–577); the consensus is that he did indeed undertake a voyage into the North Atlantic, perhaps between 512 and 530, and conceivably reaching North America. St Brendan’s Isle, the ‘Isle of the Blest’, a step before the Land of Promise, was regularly marked on early printed maps for some centuries; even if there was some doubt as to the accuracy of the account of his voyage, it was much safer for the purposes of navigation to mark an island that might not exist than omit one that did.