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.[2] 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.