¹¹Ó hÓgáin, Dáithí. Fionn Mac Cumhaill: Images of the Gaelic Hero. Dublin: Gill and Macmillan, 1988. 12-13.
When Fionn was grown he avenged the death of his father by challenging his grandfather to “single combat,” or demanding compensation. The grandfather surrendered his fortress (Aimhu) to Fionn, who used it for his principal residence thereafter.