Kenneth Jackson, based on his estimates on the survival of oral tradition, also suggested that the Ulster Cycle originated in the 4th century. Other scholars, following T. F. O'Rahilly, propose that the sagas of the Ulster Cycle derive from the wars between the Ulaid and the midland dynasties of the Connachta and the nascent Uí Néill in the 4th and 5th centuries, at the end of which the Ulaid lost much of their territory, and their capital, to the new kingdoms of the Airgíalla. Traditional history credits this to the Three Collas, three great-great-great-grandsons of Conn, who defeated the Ulaid king Fergus Foga at Achad Lethderg in County Monaghan, seized all Ulaid territory west of the Newry River and Lough Neagh, and burned Emain Macha. Fergus Foga is said to have been the last king of the Ulaid to reign there. The "Annals of the Four Masters" dates this to AD 331. O'Rahilly and his followers believe the Collas are literary doublets of the sons of Niall Noígiallach, eponymous founder of the Uí Néill, who they propose were the true conquerors of Emain in the 5th century.