Eigr. Other than the evidence that she was the daughter of Amlawd Wledig there is little old evidence for this person. Her name first appears in Geoffrey of Monmouth's History (See Other Works) as "Igerna", and then in the Brut Dingestow(See Other Works) as "Eigr"*.
In the 14th C. poem "The Birth of Arthur" it's noted that she was married to Emyr Llydaw before marrying Gwrleis* (Gorlois). In Geoffrey, Uthyr uses magic to disguise himself as Gorlois in order to get to Igerna and beget Arthur. In "The Birth of Arthur" Eigr is noted as having two daughters by Gwrleis, Gwyar (Anna in Geoffrey and Mostyn 177*) and Dioneta. Gwyar has a son Hywel by Ymer Llydaw, and two others Gwalchmei (Garwain) and Medrawd (Mordred), plus three daughters - Gracia, Graeria and Dioneta - by Lleu ap Cynfarch*. While many of these characters appear in roughly these relationships in earlier sources, this poem gives the most reasonable structure*. The Mostyn 177 genealogies give Anna as the daughter of Vthyr, and as having a daughter Nonn who gave birth to [St.]David.