2 For how can there be any other Fulness, or Principle, or Power, or God, above Him, since it is matter of necessity that God, the Pleroma (Fulness) of all these, should contain all things in His immensity, and should be contained by no one? But if there is anything beyond Him, He is not then the Pleroma of all, nor does He contain all. For that which they declare to be beyond Him will be wanting to the Pleroma, or, [in other words,] to that God who is above all things.
But that which is wanting, and falls in any way short, is not the Pleroma of all things. In such a case, He would have both beginning, middle, and end, with respect to those who are beyond Him. And if He has an end in regard to those things which are below, He has also a beginning with respect to those things which are above. In like manner, there is an absolute necessity that He should experience the very same thing at all other points, and should be held in, bounded, and enclosed by those existences that are outside of Him.
For that being who is the end downwards, necessarily circumscribes and surrounds him who finds his end in it. And thus, according to them, the Father of all (that is, He whom they call Proön and Proarche), with their Pleroma, and the good God of Marcion, is established and enclosed in some other, and is surrounded from without by another mighty Being, who must of necessity be greater, inasmuch as that which contains is greater than that which is contained. But then that which is greater is also stronger, and in a greater degree Lord; and that which is greater, and stronger, and in a greater degree Lord— must be God.
Source: Adversus haereses (New Advent)