AbstractThe Island of the Mighty, by Evangeline Walton (1936), is one of the first modern adaptations of the Mabinogi. The novel’s re-publication in 1970 launched Walton’s career as a critically and popularly successful fantasy fiction writer. Although her work is little-known today, the re-publication of The Mabinogion Tetralogy (2001) indicates a renewed interest in this ground-breaking work. This essay examines the novel’s feminist re-visioning of Arianrhod’s virginity test in the Fourth Branch as a case study for Walton’s ability to re-examine the Mabinogi from a modern perspective while maintaining a fidelity to the medieval narrative. Walton’s re-visioning focuses on the transformation of gender roles in a Mother Goddess-worshipping culture on the verge of monotheism, as the pagan traditions of the Old Tribes are slowly eroded by the patriarchal New Tribes. The novel utilizes the virginity test as an exemplar of this emerging patriarchy’s desire to place the formerly venerated female body under its masculine jurisdiction.This essay will utilize Luce Irigaray’s theory of the maternal function of the female gender to explore how Arianrhod’s decision to reject the maternal role undermines both Gwydion’s gender identity and necessitates her vilification in the eyes of the Mabinogi’s medieval redactor. Walton’s re-visioning of the extant version of the Fourth Branch re-casts Arianrhod not as villain, but as a complex anti-heroine, allowing the reader to question the patriarchal gender constructs in the medieval tale and their own society.