Long, long ago, before the idea called history evolved, there existed a sexless entity called the Adi-Buddha or Primordial Buddha. From ‘Him’ emerged the duality which was to be the potential progenitor of all creation. This dual element is visualized in Buddhist aesthetics either as the deity Vajrasattva or Vajradhara.

VajrasattvaThe significant characteristic common to them is the bell (female) and thunderbolt (male), which they hold in their hands. These deities are believed to be two expressions of the same principle, and the wellspring of all creation.

The above hierarchy is essentially spiritual. It represents an idealized abstract state, graspable only to those on an elevated mental plane.

via The Five Meditating Buddhas – An Enquiry into Spiritual Aesthetics.