Both the City of Man and the City of God have their origins in the book of Genesis, Chapter 4 and Chapter 5 respectively.
Cain, the first human murderer (4:8) and the first human liar (4:9), built the first City of Man and named it after his firstborn son, Enoch (4:17),
Another Enoch, seventh from Adam in the godly line, walked with God for three hundred years (5:22) and then did not die, but was taken by God (5:24).
It would seem that he was the first human inhabitant of an eternal, heavenly city, the City of God.
Hebrews, Chapter 11 gives us some idea of the early existence of the City of God.
Abraham looked for a city which hath foundations, whose builder and maker is God (11:10). The patriarchs desired a heavenly country, and God had prepared a city for them (11:16).
And Enoch who did not see death, but was translated, is mentioned in this chapter with the patriarch and the other great men of old saved by faith (11:5).
