Most of the localities which occur in the Tale of Branwen are too well known to need any description; one or two, however, require a slight notice. Harlech is also called Twr Bronwen, or Branwen's Tower. The name of Caer Collwyn was also bestowed upon it after Collwyn ab Tangno, chief of one of the fifteen Noble Tribes of North Wales. It possesses the ruins of a fine castle. Harlech stands on the sea coast, on the confines of Ardudwy, one of the six districts of Merionethshire, of which the portion called Dyffryn Ardudwy is a remnant of the Cantrev y Gwaelod, inundated in the time of Gwyddno Garanhir.