c. 198–203 · Tertullian, On Baptism (De baptismo) 8
Over the waters of baptism, recognising as it were His primeval seat, He reposes: (He who) glided down on the Lord “in the shape of a dove,” in order that the nature of the Holy Spirit might be declared by means of the creature (the emblem) of simplicity and innocence, because even in her bodily structure the dove is without literal gall. And accordingly He says, “Be ye simple as doves.” Even this is not without the supporting evidence of a preceding figure. For just as, after the waters of the deluge, by which the old iniquity was purged—after the baptism, so to say, of the world—a dove was the herald which announced to the earth the assuagement of celestial wrath, when she had been sent her way out of the ark, and had returned with the olive-branch, a sign which even among the nations is the fore-token of peace; so by the self-same law of heavenly effect, to earth—that is, to our flesh—as it emerges from the font, after its old sins flies the dove of the Holy Spirit, bringing us the peace of God, sent out from the heavens where is the Church, the typified ark.