For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and deity; so that they are without excuse:
All Commentaries on Romans 1:20 Go To Romans 1
Augustine of Hippo
AD 430
Notice that Paul does not call them ignorant of the truth but says that they held the truth in iniquity, and he does not fail to answer the obvious question: How could those to whom God had not given the law have a knowledge of the truth? For he says that through the visible things of the creation they reached an understanding of the invisible things of the Creator.