De Opificio Mundi

And after the shining forth of that light, perceptible only to the intellect, which existed before the sun, then its adversary darkness yielded, as God put a wall between them and separated them, well knowing their opposite characters, and the enmity existing between their natures. In order, therefore, that they might not war against one another from being continually brought in contact, so that war would prevail instead of peace, God, turning want of order into order, did not only separate light and darkness, but did also place boundaries in the middle of the space between the two, by which he separated the extremities of each. For if they had approximated they must have produced confusion, preparing for the contest, for the supremacy, with great and unextinguishable rivalry, if boundaries established between them had not separated them and prevented them from clashing together,

and these boundaries are evening and morning; the one of which heralds in the good tidings that the sun is about to rise, gently dissipating the darkness: and evening comes on as the sun sets, receiving gently the collective approach of darkness. And these, I mean morning and evening, must be placed in the class of incorporeal things, perceptible only by the intellect; for there is absolutely nothing in them which is perceptible by

But when light came, and darkness retreated and yielded to it, and boundaries were set in the space between the two, namely, evening and morning, then of necessity the measure of time was immediately perfected, which also the Creator called day. and He called it not the first day, but one day; and it is spoken of thus, on account of the single nature of the world perceptible only by the intellect, which has a single nature.

The incorporeal world then was already completed, having its seat in the Divine Reason; and the world, perceptible by the external senses, was made on the model of it; and the first portion of it, being also the most excellent of all made by the Creator, was the heaven, which he truly called the firmament, as being corporeal; for the body is by nature firm, inasmuch as it is divisible into three parts; and what other idea of solidity and of body can there be, except that it is something which may be measured in every direction? therefore he, very naturally contrasting that which was perceptible to the external senses, and corporeal with that which was perceptible only by the intellect and incorporeal, called this the firmament.