[W, Ambrosius's fort].
Welsh name for the hill-fort on the southern fringes of Mount Snowdon in Gwynedd, with Arthurian and other legendary associations; also known as Braich y Ddinas. Named for Emrys Wledig [the prince, land-holder; (L Ambrosius Aurelianus], the boy-prophet who confronts Vortigern and his magicians on this site. Archaeological excavation has revealed settlement from Roman times, habitation during the 5th century, and evidence of what was once a nearby pool.
According to the best-known story, Vortigern's attempts to build a tower fail when materials disappear at night and walls collapse. His magicians recommend human sacrifice, with blood from a ‘fatherless boy’ to caulk the foundations. Before the boy can be killed he reveals the existence of an underground pool and two dragons in a stone chest, continually fighting; the dragons are explained as the Britons and the Saxons, to whom Vortigern has sold his kingship. In Historia Brittonum (9th cent., formerly attributed to Nennius) the boy's name is Ambrosius Aurelianus; in Geoffrey of Monmouth (12th cent.) he is Merlin. Vortigern gives the fortress to the boy.