The Second Day
One water, then two, and a heaven between them. Scroll to watch the firmament open.
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters: and it was so. And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament. And God called the firmament Heaven: and God saw that it was good. And the evening and the morning were the second day.
Genesis 1:6-8
"God said," Moses continues, "Let there be a firmament!" and this firmament instantaneously becomes real by the operation of the Word, and God gives it the name of 'heaven'.
Cyril of Alexandria, Against Julian Book II
Scripture as St Theophilus of Antioch sets it down in To Autolycus. Both texts are from the Forge library.