Folklorist Resurrección María de Azkue ties Mari Urraca to a legend about a princess of the Kingdom of Navarre, widow of a 12th-century nobleman who lived in the Tower of Muncharaz in the valley known as the Merindad de Durango. She vanished at the time of his death and was said to have headed for the cave of Anboto. According to Azkue, Iturriza tells this story in his Historia de Vizcaya. Labayru in her Historia de Vizcaya doubts it.