Such identification of a mere mortal country with the other world seems strange enough to us, but to our Celtic ancestors it was a quite natural thought. All islands—and peninsulas, which, viewed from an opposite coast, probably seemed to them islands—were deemed to be pre-eminently homes of the dark Powers of Hades. Difficult of access, protected by the turbulent and dangerous sea, sometimes rendered quite invisible by fogs and mists and, at other times, looming up ghostlily on the horizon, often held by the remnant of a hostile lower race, they gained a mystery and a sanctity from the law of the human mind which has always held the unknown to be the terrible. The Cornish Britons, gazing from the shore, saw Gower and Lundy, and deemed them outposts of the over-sea Other World. To the Britons of Wales, Ireland was no human realm, a view reciprocated by the Gaels, who saw Hades in Britain, while the Isle of Man was a little Hades common to them both. Nor even was the sea always necessary to sunder the world of ghosts from that of “shadow-casting men”. Glastonbury Tor, surrounded by almost impassable swamps, was one of the especial haunts of Gwyn ap Nudd. The Britons of the north held that beyond the Roman wall and the vast Caledonian wood lived ghosts and not men. Even the Roman province of Demetia—called by the Welsh Dyfed, and corresponding, roughly, to the modern County of Pembrokeshire—was, as a last stronghold of the aborigines, identified with the mythic underworld. As such, Dyfed was ruled by a local tribe of gods, whose greatest figures were Pwyll, “Head of Annwn” (the Welsh name for Hades), with his wife Rhiannon, and their son Pryderi. These beings are described as hostile to the children of Dôn, but friendly to the race of Llyr. After Pwyll’s death or disappearance, his widow Rhiannon becomes the wife of Manawyddan.[322] In a poem of Taliesin’s we find Manawyddan and Pryderi joint-rulers of Hades, and warders of that magic cauldron of inspiration[323] which the gods of light attempted to steal or capture, and which became famous afterwards as the “Holy Grail”. Another of their treasures were the “Three Birds of Rhiannon”, which, we are told in an ancient book, could sing the dead to life and the living into the sleep of death. Fortunately they sang seldom. “There are three things,” says a Welsh triad, “which are not often heard: the song of the birds of Rhiannon, a song of wisdom from the mouth of a Saxon, and an invitation to a feast from a miser.”