Sant Eilian was sent to Anglesey as a missionary. The Prince of Gwynedd stole Eilian's cattle and in retaliation, Eilian struck the prince blind. The prince showed some remorse and in return for his sight, would give Eilian the amount of land that his deer could cover before being brought down by the prince's greyhounds.

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Eilian restored the prince's sight and released his deer who sped across the fields. The greyhounds kept chase but the deer was able to leap across a large gorge. This resulted in Eilian gaining a large amount of land and he became known as a healer of eye ailments. The gorge near Amlwch is still known in Welsh as 'Llam Carw' (Deer's Leap).