One of the Cerrigmarchogion cairns

King Arthur is asked to help Culhwch win the hand of Olwen , daughter of the giant Yspaddaden Pencawr / Is set a series of tasks / One to hunt down the giant boar Twrch Trwyth /
The Boar is pursed across Ireland and out into the Irish Sea / coming ashore at Porth Clais and on to the Preseli Mountains .

Cerrigmarchogion " Rock of the Knights ", where the mythical Boar - " Twrch Trwyth " slew several of King Arthur's Knights and then turned them into stone .