It is necessary, therefore, to preserve the series of generations descending from Shem, for the sake of exhibiting the city of God after the flood; as before the flood it was exhibited in the series of generations descending from Seth. And therefore does divine Scripture, after exhibiting the earthly city as Babylon or Confusion,
But to avoid needless prolixity, we shall mention not the number of years each member of this series lived, but only the year of his life in which he begot his heir, that we may thus reckon the number of years from the flood to Abraham, and may at the same time leave room to touch briefly and cursorily upon some other matters necessary to our argument. In the second year, then, after the flood, Shem when he was a hundred years old begot Arphaxad; Arphaxad when he was 135 years old begot Cainan; Cainan when he was 130 years begot Salah. Salah himself, too, was the same age when he begot Eber. Eber lived 134 years, and begot Peleg, in whose days the earth was divided. Peleg himself lived 130 years, and begot Reu; and Reu lived 132 years, and begot Serug; Serug 130, and begot Nahor; and Nahor 79, and begot Terah; and Terah 70, and begot Abram, whose name God afterwards changed into Abraham. There are thus from the flood to Abraham 1072 years, according to the Vulgate or Septuagint versions. In the Hebrew copies far fewer years are given; and for this either no reason or a not very credible one is given.
When, therefore, we look for the city of God in these seventy-two nations, we cannot affirm that while they had but one lip, that is, one language, the human race had departed from the worship of the true God, and that genuine godliness had survived only in those generations which descend from Shem through Arphaxad and reach to Abraham; but from the time when they proudly built a tower to heaven, a symbol of godless exaltation, the city or society of the wicked becomes apparent. Whether it was only disguised before, or non-existent; whether both cities remained after the flood, — the godly in the two sons of Noah who were blessed, and in their posterity, and the ungodly in the cursed son and his descendants, from whom sprang that mighty hunter against the Lord, — is not easily determined. For possibly — and certainly this is more credible — there were despisers of God among the descendants of the two sons, even before Babylon was founded, and worshippers of God among the descendants of Ham. Certainly neither race was ever obliterated from earth. For in both the Psalms in which it is said, They are all gone aside, they are altogether become filthy; there is none that does good, no, not one, we read further, Have all the workers of iniquity no knowledge? Who eat up my people as they eat bread, and call not upon the Lord. There was then a people of God even at that time. And therefore the words, There is none that does good, no, not one, were said of the sons of men, not of the sons of God. For it had been previously said, God looked down from heaven upon the sons of men, to see if any understood and sought after God; and then follow the words which demonstrate that all the sons of men, that is, all who belong to the city which lives according to man, not according to God, are reprobate. — from The City of God