Leslie Stephen,
Dictionary of National Biography…
(1894)
“ MERLIN AMBROSIUS, or MYRDDIN EMRYS, legendary enchanter and bard, is first to be definitely traced in the ‘Historia Brittonum’ ascribed to Nennius, a work which seems to date from the end of the eighth century (Zimmer, Nennius Vindicatus) . Nennius relates that the wise men had told Vortigern that he could not build his castle on Snowdon unless the foundations were sprinkled with the blood of a child that had no father. ”
