Cormac mac Cuilennáin, king-bishop of Cashel, compiled a glossary around the year 900. It is the earliest dictionary in any non-classical European language. In it, Cormac describes Manannán as "a celebrated merchant who was in the Isle of Man. He was the best pilot that was in the west of Europe. He used to know by studying the heavens the period which would be fine weather and the bad weather, and when each of these two times would change."

A weather forecaster. The god of the sea, the ruler of the Otherworld, the one who could make a single man look like a thousand — reduced to a merchant with a knack for reading clouds.

This is what scholars call euhemerisation: taking a divine figure and rewriting him as a historical person. Christian scribes did it routinely. They could not have pagan gods in their manuscripts, so the gods became kings, or merchants, or clever men who could read the sky. The storms became weather forecasting. The Otherworld became a trade route. Moore, writing in 1891, traces the process clearly: as early as the ninth and tenth centuries Manannán "had suffered the change known as euhemerisation, from an immortal he had become a mortal." Yet the Voyage of Bran, written a century before Cormac, has Manannán riding a chariot across the ocean and seeing flowery plains where mortals see waves. The earlier text is more mythological, not less. The reduction came afterwards, deliberately. Someone decided to make the god smaller.

It did not work. The fog still comes in from the south. The rushes still go up the hill. The fishermen of Peel and Port St Mary, for centuries, went to sea with an understanding that the sea belonged to someone, and you did not go out on it without acknowledgement.