Ancient gnosticism used the ancient cosmic system: The earth was in the center, surrounded by the air and spheres: sun, moon, Mercury, Venus, Mars, Jupiter, Saturn, and a ring of fixed stars that close it all off.
That was more-or-less accepted astronomical science around the time of Christ. It was nothing novel.
But the ancient gnostic took the cosmological system one step further: it taught that the cosmological system was a prison.
Every ancient gnostic sect taught this idea. Most sects said the cosmos was the creation of an evil god, the “Demiurge,” who created the cosmos as a structure of deception. The Demiurge then outfitted the structure with demons and archons who acted as prison guards to make sure no one got out of this cosmological prison.
Gnosticism offered liberation from the prison. The cosmological prison was the sine qua non of gnosticism: If existence wasn’t a prison, the gnostic’s product—knowledge, the map, the plan for escaping the prison—was worthless.
Gnosticism without a structural evil to overcome is like football, baseball, or basketball without a ball.