E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
By a Papal enactment made in the middle of the ninth century, the figure of a cock was set up on every church-steeple as the emblem of St. Peter. The emblem is in allusion to his denial of our Lord thrice before the cock crew twice. On the second crowing of the cock the warning of his Master flashed across his memory, and the repentant apostle went out and wept bitterly.