What about Romans 1:20? "For the unseen things of Him from the creation of the world are clearly seen, being understood by the things made [poiema]"
 
God has been known among the heathens SINCE "the creation of the world". But was he known by the "things that are made [poiema]"?
 
The word poiema is found thirty times in the Greek version of the Old Testament. Except for one occurrence it translates the Hebrew word ma'aseh, "deed" or "work". In one exception it translates the Hebrew po'al, "doing", "deed" or "work".  (1)
 
The noun poiema is in the plural. In classical Greek the word is used in the plural to refer to works, to poems, to fiction, deeds or acts -- i.e., anything made or done. (2)
 
(1) and (2) are taken from the Wycliffe Bible Commentary 1962, p1186 
 
 
Clearly, there are several ways of translating Romans 1:20.
 
Instead of translating it, God was known "by the things made [poiema]", it could be translated -- God was known "by the things done [poiema]".
THOUGHTS ON ROMANS 1
God has revealed Himself to the unregenerate Gentiles to CONDEMN them. "The unseen things of Him ... are clearly seen ... for them to be without excuse."

In this passage, Paul implies that if God was not revealed among then Gentiles, the Gentiles would have an excuse. Christ Himself makes this point with the Pharisees. " If I came not and speak to them, they had no sin. Yet now they have no pretense concerning their sin." (John 15:22). Christ is saying that IF there is no revelation, then there is no condemnation. The darkness can only be condemned by the light.

Thus, if God had not revealed Himself to the Gentiles, then He would be unjust in punishing them for their sins. "For where no Law is, there is no transgression." Paul says the ONLY way he knew that lust was sin was BY THE LAW. "By the Law is the knowledge of sin." Of course the Gentiles did not have the Law of Moses. But they DID have ENOUGH of the Moral Law to be condemned as rebellious sinners. Paul notes that " those who, recognizing the just statute of God, that those committing such things are deserving of death, not only are doing them, but are endorsing, also, those who are committing them." (Concordant Literal). The Gentiles KNEW ABOUT the just statutes of God.  God DID reveal Himself to them "FOR THEM TO BE WITHOUT EXCUSE."

Now, the question is raised -- how did God communicate this information to the Gentiles? Paul says  "For the unseen things of Him from the creation [ktisis ] of the world are clearly seen..."

As you are well aware, I don't think Paul is saying that the Gentiles knew about God by looking at trees and rocks. I think he is saying that *from the beginning of creation* or *from the foundations of the world*, Gentiles have known about the True God. Otherwise, how do you make sense of Hebrews 11? It's says that it is BY FAITH that we know that the worlds were framed by the Word of God and not from the things that do appear. This would mean that unregenerate Gentiles -- without faith -- CANNOT possess the Scriptural knowledge that the worlds were created. Of course, they will HEAR the truth OUTWARDLY, but they do not know it internally in their conscience. The doctrine of creation is NOT obvious. Only God can reveal it to man.

This is the right time to return to the original question -- how did God communicate this information to the Gentiles? Paul says  "For the unseen things of Him from the creation [ktisis] of the world are clearly seen..."

There are similar expressions in the New Testament to Paul's phrase, "from the creation of the world". Here are four samples --

"But from the beginning of creation [ktisis ] "God made them male and female." Gen. 1:27 (Mark 10:6).

"...during the last days scoffers will come walking according to their own lusts, and saying, Where is the promise of His coming? For from which time the fathers fell asleep, all things remain so from the beginning of creation [ ktisis ]." (2 Pet 3:3-4).

Notice also that the expression, "from the creation of the world" is very similar to the phrase, "from the foundation of the world."

"Jesus spoke all these things in parables to the crowds, and He did not speak to them without a parable,
so that was fulfilled that spoken through the prophet, saying: "I will open My mouth in parables; I will speak out things hidden from the foundation of the world." Psa. 78:2" (Matthew 13:34-35)

"And all those dwelling in the earth will worship it, those of whom the names had not been written in the Book of Life of the Lamb having been slain from the foundation of the world ... And those dwelling on the earth will marvel, the ones whose names have not been written on the Book of Life from the foundation of the world, seeing the beast, that it was a thing, and is not, yet now is." (Revelation 13:8, 17:8)

I hope it's clear from the Scripture above what Paul means when he says, "For the unseen things of Him from the creation [ktisis] of the world are clearly seen from the things that are made...". He's saying that it is from the BEGINNING of creation that men have known about the True God. It's from the foundations of the world that God's truth has been manifested among men.

So, what does Paul mean when he says "the unseen things of Him .... are clearly seen from the things that are made [poiEma]". The Greek word poiEma only occurs twice in the New Testament. The other place is Ephesians 2:10.

"for we are His workmanship [poiEma], created in Christ Jesus unto good works" (LITV)

" For His achievement are we, being created in Christ Jesus for good works." (Concordant Literal translation)

At this point, I'd like to post the Concordant Literal translation of Romans 1. Whilst I in NO WAY endorse the other writings of Concordant Publishing, their translations are remarkably literal.

18 For God's indignation is being revealed from heaven on all the irreverence and injustice of men who are retaining the truth in injustice,
19 because that which is known of God is apparent among [en] them, for God manifests it to them.
20 For His invisible attributes are descried from the creation of the world, being apprehended by His achievements, besides His imperceptible power and divinity, for them to be defenseless,
21 because, knowing God, not as God do they glorify or thank Him, but vain were they made in their reasonings, and darkened is their unintelligent heart. ( http://www.concordant.org/version/index.html )

The translation of the 19th verse seems justified if we look at other Scripture where the Greek word en is used in a similar context to Romans 1. " That which is known of God is apparent among [en] them, for God manifests it to them." Surely, God does not reveal himself INSIDE the minds of the unregenerate !! No more than the Kingdom of Heaven was inside the unregenerate Pharisees---

" And being questioned by the Pharisees ...He answered them and said, ... the kingdom of God is IN [ en] YOUR MIDST" (LITV, Luke 17:20:21)

Thus, as revelation was known AMONG the unregenerate Jews, so it was AMONG (not inside!) the Gentiles. Both had it "in their midst", and will be held accountable.

There is a similiar use of the Greek in Luke chapter 1. Mary was blessed among [en] women. Likewise the truth is known among [en] the Gentiles.

"And entering, the angel said to her, .... You are blessed AMONG [en] women!" (LITV, Luke 1:28).

*****To sum up -- the True was God known AMONG the Gentiles by His achievements and His Moral Law. This means that ALL Gentiles are condemned for disobeying God's revealed will. If they did not have the revelation, they would not have been condemned. But God was MANIFESTED among them by the spread of information (by word of mouth, preachers, dispersed Jews, proselyte Gentiles), i.e. the spread of Scriptural information. The darkness IS condemned by the light.

And remember how I pointed out the similarity with Christ's reasoning. He said, " If I came not and speak to them, they had no sin. Yet now they have no pretense concerning their sin." (John 15:22). Well, I'd like to put this verse in the context of another two verses from John.

In the first passage, Christ states that the Jews knew about the True God:

"Then teaching, Jesus cried out in the temple, even saying, You both know Me, and you know from where I am. And I have not come from Myself, but He is true, the One having sent Me, whom you do not know." (John 7:28).

This is similar to what Paul states about the Gentiles in Romans 1. Perhaps, he could have said something like this to the Gentiles: "You have known about the True God ... His knowledge was manifested among you from the start of time ... AND YOU ARE WITHOUT EXCUSE for your wicked response to his revelation..."

Yet, in another sense, Christ could say that the Jews did NOT know God (and Paul could likewise say that the Gentiles "knew not God.").

"Then they said to Him, Where is your father? Jesus answered, You neither know Me, nor My Father. If you had known Me, then you also would have known My Father." (John 8:19).

The Pharisees claimed to believe in "The Father", but Christ emphatically denies they know about Him at all. Keeping in mind Christ's previous statements, He must be saying that the Pharisees were INTERNALLY darkened -- they did not have the Holy Spirit in their consciences to convict them of the truth.

And it was no better with the unregenerate Gentiles. Indeed, Paul said that prior to their conversions, the Galatians , "...indeed, NOT KNOWING GOD, you served as slaves to the ones by nature not being gods."

Without the doctrine of inspiration, you can have no knowledge of God abiding in your mind. You can only have opinions and speculations about what you call "God." The Holy Spirit is required to SEAL, WITNESS and CONVICT a person of the PROPOSITIONS of Scripture in order for that person to have the knowledge of God abiding in their minds. "He that believes God has the witness in Himself ... has set to His seal that God is true ..." And because saving faith is always a SURPRISING CHANGE OF MIND, when an elect sinner is converted they KNOW IT WITHOUT A DOUBT. "They shall hear a voice coming behind them in the desert ..." and the voice of God is the words of Scripture.

This is the basis of assurance of salvation. Since an elect sinner is TOTALLY in the dark of God's existence (in terms of KNOWING it with certainty), then when the LIGHT of the gospel shines into his mind for the first time, he will know that he is justified by Christ's work. After all, God has certified that EVERYONE believing the gospel record "IS justified," "IS born of God," and "will NOT come into judgment."

John 5:24 "Truly, truly, I say to you, The one who hears My Word, and BELIEVES the One who has sent Me, HAS EVERLASTING LIFE, and does not come into judgment, but has passed out of death into life."

In John 5:24, you can see God JOINING together BELIEF and JUSTIFICATION. Everyone who believes the facts of the gospel, "does not come into judgment."  Now, according to the Apostle John, this declaration -- that believers are justified -- is THE WITNESS.

"And this is the witness: that God gave us everlasting life, and this life is in His Son." (1 John 5:11)

Notice that John uses the word, "us". He gave "us" -- believers -- everlasting life. In other words, if someone does NOT know they are a believer, they cannot say, "God have given me / us everlasting life." They are not confessing full assurance of salvation, like the Apostle John did. They do not have the faith of the Apostles. And anyone without the FAITH OF THE APOSTLES is damned. Peter ONLY wrote to those, who had "obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ." (2 Peter 1:1, KJV)

If your assurance does not match that of the Apostles, you are lost. You are calling God a liar. God says that ALL believers will be saved, and you are saying, "I'm a believer, but I do not know that I'm saved." Well, God says EVERYONE who believes that Christ was risen from the dead IS SAVED (Romans 10). Clearly, you are IGNORANT of this promise.

"The one not believing God has made Him a liar, because he has not believed in the witness which God has witnessed concerning His Son." (1 John 5: 10).