What A Catholic Pope Taught On Capital Punishment

Pope St. Leo the Great, Letter 15, July 21, 447: “[On the Priscillianists] Rightly then our fathers, in whose times this abominable heresy sprung up, promptly pursued it throughout the world, that the blasphemous error might everywhere be driven from the Church: for even the leaders of the world so abhorred this profane folly that they laid low its originator, with most of his disciples, by the sword of the public laws.  For they saw that all desire for honorable conduct was removed, all marriage-ties undone, and the Divine and the human law simultaneously undermined, if it were allowed for men of this kind to live anywhere under such a creed.  And this rigorous treatment was for long a help to the Church's law of gentleness which, although it relies upon the priestly judgment, and shuns blood-stained vengeance, yet is assisted by the stern decrees of Christian princes...”