These were left to the secondary powers,--the spirits.

Hence it happens that by the side of the great gods, we have a large number of minor powers who preside over the various branches of human handiwork and control the products of the human mind.
Reserving further details regarding the several classes of demons and spirits enumerated, it will suffice to say a few words about one particular group of spirits whose role was peculiarly prominent in both historical, liturgical, and general religious texts.

The tendency to systematize the beliefs in spirits manifests itself in Babylonia, equally with the grouping of the gods into certain classes.

In consequence of this general tendency, the conception arose of a group of spirits that comprised the associated secondary powers of earth and heaven, somewhat as Anu, Bel, and Ea summed up the quintessence of the higher powers or gods.

This group was known as the Anunnaki and Igigi.
Regarding these names it may be said that the former has not yet been satisfactorily interpreted.