Next, He split all this that He had put together into two parts lengthwise; and then He laid the twain one against the other, the middle of one to the middle of the other, like a great cross; and bent either of them into a circle, and join them, each to itself and also to the other, at a point opposite to where they had first been laid together. And He compassed them about with the motion that revolves in the same spot continually, and He made the one circle outer and the other inner. And the outer motion He ordained to be the Motion of the Same, and the inner motion the Motion of the Other. And He made the Motion of the Same to be toward the right along the side, and the Motion of the Other to be toward the left along the diagonal; and He gave the sovranty to the Revolution of the Same and of the Uniform. For this alone He suffered to remain uncloven, whereas He split the inner Revolution in six places into seven unequal circles, according to each of the intervals of the double and triple intervals, three double and three triple. These two circles then He appointed to go in contrary directions; and of the seven circles into which He split the inner circle, He appointed three to revolve at an equal speed, the other four to go at speeds equal neither with each other nor with the speed of the aforesaid three, yet moving at speeds the ratios of which one to another are those of natural integers.
And when the construction of the Soul had all been completed to the satisfaction of its Constructor, then He fabricated within it all the Corporeal,and uniting them center to center He made them fit together. And the Soul, being woven throughout the Heaven every way from the center to the extremity, and enveloping it in a circle from without, and herself revolving within herself, began a divine beginning of unceasing and intelligent life lasting throughout all time. And whereas the body of the Heaven is visible, the Soul is herself invisible but partakes in reasoning and in harmony, having come into existence by the agency of the best of things intelligible and ever-existing as the best of things generated.
~Timeaus, Plato
And when the construction of the Soul had all been completed to the satisfaction of its Constructor, then He fabricated within it all the Corporeal,and uniting them center to center He made them fit together. And the Soul, being woven throughout the Heaven every way from the center to the extremity, and enveloping it in a circle from without, and herself revolving within herself, began a divine beginning of unceasing and intelligent life lasting throughout all time. And whereas the body of the Heaven is visible, the Soul is herself invisible but partakes in reasoning and in harmony, having come into existence by the agency of the best of things intelligible and ever-existing as the best of things generated.
~Timeaus, Plato
In discussing the creation and nature of the universe, Timeaus/Plato has the demiurge set the physical world with two great circular bands, fastening them together so that they form two intersect portions on either side. It is from these two points that the World Soul gives to the material universe the phenomenon of motion, time, and life.
It's generally understood that Plato was in fact discussing the two bands of the zodiac and the ecliptic. (Although some have argued that it the ecliptic and Milky Way).
This idea extended beyond Plato, however. Similar crosses (saltire) appear throughout the ancient world:
Urania, the muse of astronomy, and the globe etched with a cross
Coins minted during the reign of Domitian.His son sits on a globe etched with cross surrounded by seven stars.
The lion-headed god of Mithraism, interpreted to be the demiurge, stands upon a globe etched with a cross
Apollo, Pompeii, holds a globe etched with a cross
Helios holding a globe etched with a cross, from a fourth century synagogue
So it seems easy to see where certain Gnostic sects got their idea of a Heavenly/celestial cross.
He showed me a cross of light fixed, and about the cross a great multitude, not having one form: and in it was one form and one likeness. And the Lord himself I beheld above the cross, not having any shape, but only a voice: and a voice not such as was familiar to us, but one sweet and kind and truly of God, saying unto me: John, it is needful that one should hear these things from me, for I have need of one that will hear. This cross of light is sometimes called the word by me for your sakes, sometimes mind, sometimes door, sometimes a way, sometimes bread, sometimes seed, sometimes resurrection, sometimes Son, sometimes Father, sometimes Spirit, sometimes life, sometimes truth, sometimes faith, sometimes grace. And by these names it is called as toward men: but that which it is in truth, as conceived of in itself and as spoken of unto you, it is the marking-off of all things, and the firm uplifting of things fixed out of things unstable, and the harmony of wisdom, and indeed wisdom in harmony. There are of the right hand and the left, powers also, authorities, lordships and demons, workings, threatenings, wraths, devils, and the lower root whence the nature of the things that come into being proceeded. This cross, then, is that which fixed all things apart by the word, and separate off the things that are from those that are below, and then also, being one, streamed forth into all things. But this is not the cross of wood which thou wilt see when thou goest down hence.
Apocryphon of John
Apocryphon of John
But a heavenly crucifixion?
Yes!
It is by gods' work that they say Ixion,
fixed on his winged wheel, spun in a circle,
cries aloud ...
Zeus likewise wrought the crucifixion on the wheel,
Ixion's bane; and, spinning there,
limbs fast to the ineluctable circle
Victory Odes, Pindar
fixed on his winged wheel, spun in a circle,
cries aloud ...
Zeus likewise wrought the crucifixion on the wheel,
Ixion's bane; and, spinning there,
limbs fast to the ineluctable circle
Victory Odes, Pindar
And yes, Ixion was, in some traditions, NAILED to the wheel, as Plutarch observed in his Moralia:
Now these judgments and opinions conveyed in the words (of a poet) are easy to notice for anyone who pays attention. But they (i.e. the poets) also provide lessons from the actions themselves (that they portray). Thus Euripides is said to have answered those who criticized his Ixion for being impious and impure by saying, ‘But I did not bring him off the stage before I had nailed him to the wheel.’