In the mythical cosmogony of Hesiod (8th-7th century BC) the origin of the world is an unlimited void which is called chaos.This is described as a large gap without bottom. (abyss)(The original greek word is gaping void,but later formless state and complete disorder.)
In the ancient Greek philosophy, arche (ἀρχή) is the beginning or the first principle of the world. The idea of an arche was first philosophized by Thales of Miletus (7th-6th century BC), who claimed that the first principle of all things is water. His theory was supported by the observation of moisture throughout the world and coincided with his theory that the earth floated on water.Pherecydes of Syros (6th century BC),another greek philosopher believed that the origin was water and called it also chaos..These ideas were influenced by the Babylonian creation story Enuma Elish,where the creation begins with the universe in a formless state.Tiamat is the personification of salt water and she formed all things..Some scholars believe that in the original book of the bible the universe was also in a formless state and the only existing thing was the water abyss. In the official translation Vulgate the earth "was without form and void and darkness was upon the face of the deep".
Thales' theory was refuted by his successor and esteemed pupil, Anaximander. Anaximander noted that water could not be the arche because it could not give rise to its opposite, fire. Anaximander claimed that none of the elements (earth, fire,air,water) could be arche for the same reason. Instead, he proposed the existence of the apeiron, an indefinite substance from which all things are born and to which all things will return.Apeiron (endless or boundless) is something completely indefinite and Anaximander was propably influenced by the original chaos of Hesiod.
Anaximenes, Anaximander's pupil, advanced yet another theory. He returns to the elemental theory, but this time posits air, rather than water, as the arche. Anaximenes suggests that all is made from air through either rarefication or condensation (thinning or thickening). Rarefied, air becomes fire; condensed, it becomes first wind, then cloud, water, earth, and stone in order. The Arche is technically what underlies all of reality/appearances.