According to the notion prevalent among the Greeks and Romans, the sky was a great vault of crystal to which the fixed stars were attached, though by some it was held to be of iron or brass. That the Hebrews entertained similar ideas appears from numerous biblical passages. In the first account of the creation (Genesis 1) we read that God created a firmament to divide the upper or celestial from the lower or terrestrial waters. The Hebrew means something beaten or hammered out, and thus extended; the Vulgate rendering, "firmamentum" corresponds more closely with the Greek stereoma (Septuagint, Aquila, and Symmachus), "something made firm or solid". The notion of the solidity of the firmament is moreover expressed in such passages as Job 37:18, where reference is made incidentally to the heavens, "which are most strong, as if they were of molten brass".
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In conformity with these ideas, the writer of Genesis 1:14-20 represents God as setting the stars in the firmament of heaven, and the fowls are located beneath it, i.e. in the air as distinct from the firmament. On this point as on many others, the Bible simply reflects the current cosmological ideas and language of the time.