Caer Ibormeith was the Celtic goddess of sleep and dreams. In Irish mythology, Caer Ibormeith was a daughter of Prince Ethal Anbuail of Sid Uamuin in Connacht. Every alternate Samhain she would change into a swan, in which form she would remain for a year before becoming human again the following Samhain. She eventually married Aengus of the Tuatha de Dannan, but first he had to pick her out, in swan form, from a group of one hundred and fifty other swans at Loch Bel Dragon (Now Lough Muskry in the Galtees.) Having chosen correctly, he turned into a swan himself and they flew away, to the fortress of the River Boyne at Drogheda, singing beautiful music that put all its listeners asleep for three days and nights. With Aengus, Caer was the foster-mother of Diarmuid.