E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Rule (St.) or St. Regulus,
a monk of Patræ in Achaia, is the real saint of Scotland. He was the first to colonise its metropolitan see, and to convert the inhabitants (370). The name Killrule (Cella Reguli) perpetuates this fact. St. Andrew superseded the Achæan.