Leil was a peaceful and just king and took advantage of the prosperity afforded him by his ancestors. He founded Carlisle, Cumbria (Caerleil: Fort of Leil) in the north as a tribute to this prosperity. He reigned for twenty-five years until he grew old and feeble. His inactivity sparked a civil war, during which he died. He was succeeded by his son Rud Hud Hudibras.
- Marjorie Chibnall (ed), Anglo-Norman Studies: Proceedings of the Battle Conference, Volume: 13, Boydell Press, Woodbridge, 1983, p.109.