22Andersen, Jørgen. The Witch on the Wall: Medieval Erotic Sculpture in the British Isles. Copenhagen: Rosenkilde and Bagger, 1977. 14+.
Anderson considers the sheela-na-gig carvings to be Romanesque (c. 1100 CE). Maureen Concannon disagrees, and entertains the possibility that the carvings pre-date the structures on which they are mounted: "Many of the carvings on those buildings are noticeably more worn than the rest of the stone work, indicating that they were probably transferred from the earlier structures to the later churches. This would be in accord with the veneration in which the people would have held those sacred stones and points once again to the conservatism of the country people of Ireland." (Concannon, Maureen. The Sacred Whore: Sheela, Goddess of the Celts. Cork: Collins, 2004. 61-2.)
Thomas Wright (The Worship of the Generative Powers, 1866) wrote that sheela-na-gigs were survivals of a pre-Christian fertility worship. In some ways, the effort to see the sheela-na-gigs as a remnant of pre-Christian Ireland has a parallel in the views, promoted in 1833 by Henry O'Brien, to claim the Irish round towers as the creations of prehistoric Tuatha Dé Danann for their phallic-worshiping religion. See our entry on the Kildare Round Tower. (Leerssen, Joep. Remembrance and Imagination: Patterns in the Historical and Literary Representation of Ireland in the Nineteenth Century. Notre Dame, IN: University of Notre Dame in Association with Field Day, 1997. 120.)