The city of man is aware of the presence and nature of the City of God, as we see in some of the Sibylline prophecies which point to Christ (though Augustine has his doubts about some aspects of this prediction).
The philosophers followed the theological poets, including Thales. This in no way helped the city of man worship the true God, and in fact drove them farther into idolatry. King Numa of Rome is the best example of this, as he "stuffed heaven with divinities" so much "that there was no room left for him."
As the Israelites went into captivity, philosophers and law givers worked in the city of man.