When Socrates and Plato playfully questioned whether the Greek common notion of reality might be a shadow of reality, whether the Greek senses might not be akin to some narrow dark cave on which a great light shines, but the Greek mind being at the back of this cave is only able to see silouhettes against the bright light, and shadows on the back of the cave wall. What if that being the case all that we know are shadows and unclear shapes? Then the real Things that underpin our notions of reality are considered as mere " ideas" or " forms" of our reality!
Plato asks the question, not because he knows the answer, but because he knows the question has been asked and answered in 3 ancient empires before the Greek! Each of the Dravidian, Babylonian and Egyptian empires asked these questions and each came up with its own prevailing answer. For the Dravidians it was the development of a mental psychological culture that we see throughout India. For the Egyptians it was the great temple structures that marked out astronomical patterns of stars, the greater reality being the stars. And for the Babylonians it was the astrological relationships between the stars and the seasons, the meticulous astrological synchrony of every aspect of their lives with the motions of planets, stars and the sun and moon!
What would be the Greek answer?
Plato felt that the answer lay in the astrological knowledge of the Pythagoreans, the Mathematikos of the Pythagorean school. To introduce this knowledge Plato commisioned Euclid to develop a course of philosophy that took the student from his everyday surroundings to the deep philosophical questions of reality. This resulted in the Stoikeioon, the introduction to the philosophy of the Sphere. The sphere representing the very space in which all realities are disposed, according to each realities rank, with the gods being in the greatest, most high ranking sphere or spheres.
The fundamental nature of the sphere in platonic/Pythagorean philosophy and Theurgy cannot be overemphasised.