Ambrose of Milan : The second river is Gihon, by which, when they were sojourning in Egypt, was laid down the law of the Israelites that they should depart from Egypt, and having girded their loins they should as a sign of temperance partake of a lamb. It is fitting that the chaste and the sanctified should celebrate the Pasch of the Lord. For that reason, the observance of the law was first carried out beside that river, the name of which signifies an opening of the earth. Therefore, just as an opening absorbs the earth and whatever defilements and refuse there may be in it, in like manner chastity tends to consume all the passions of the body. Appropriately, then, the observance of the established law first took place there, because carnal sin is absorbed by the law. And so Gihon, which is a figure of chastity, is said to surround the land of Ethiopia in order to wash away our lowly bodies and quench the fires of our vile flesh. The meaning of Ethiopia in Latin is "holy and vile." What is more lowly, what is more like Ethiopia, than our bodies, blackened, too, by the darkness of sin? — On Paradise Bede : And the name of the second river is Geon. It is the one which goes around all the land of Ethiopia. The name of the third river is Tigris. It goes towards the Assyrians. The fourth river is Euphrates. Therefore, concerning the Euphrates, where it goes or what lands it circles, it does not say, because, flowing nearby the land of promise, it was very easily known to the people of Israel, who were placed there and were to read this. But since a return to heavenly places is open to us through the waters of regeneration, it is sufficiently fitting to the dispensation of divine piety that this very element, through which we are led back to the upper homeland, is common to us with paradise, where the first man was placed, and just as grace invisibly recreates us in preparation for the entrance to the heavenly kingdom: so also invisibly from paradise through the veins of the earth the very water through which we are recreated flows forth to the Lord's world. Just as the Spirit breathes where He wills, and you hear His voice, but do not know where it comes from or where it goes (John 3:8); thus it was fitting that the water which the Holy Spirit sanctifies those whom He wills, should come to us by unknown ways from paradise, and return to unknown places to us, because it is known to have its origin from the paradise of pleasure. — Commentary on Genesis (Hexaemeron)