The concept of an Ogdoad appears in Gnostic systems of the early Christian era, and was further developed by the theologian Valentinus (ca. 160 AD).

The number eight plays an important part in Gnostic systems, and it is necessary to distinguish the different forms in which it appeared at different stages in the development of Gnosticism. The earliest Gnostic systems included a theory of seven heavens and a supercelestial region called the Ogdoad. Astronomical theories had introduced the concept of seven planetary spheres with an eighth above them, the sphere of the fixed stars.

In the system of Valentinus, the seven heavens, and even the region above them, were regarded as but the lowest and last stage of the exercise of creative power. Above them was the Pleroma, where were exhibited the first manifestations of the evolution of subordinate existence from the great First Principle.