An Eternal flame from a Zoroastrian fire temple in Yazd, Iran. The role of fire in Heraclitean philosophy has been compared with fire worship in Zoroastrianism, the state religion of the Achaemenid Empireduring Heraclitus' life.

The Milesians before Heraclitus conceived of certain elements as the arche – Thales with water, Anaximander with apeiron, and Anaximenes with air – Many philosophers concluded that Heraclitus construed of fire as the arche, the fundamental element that gave rise to the other elements. However, it is also argued by many that he never identified Fire as the arche rather, he only use fire to explain his notion of flux.[47][ba] Pre-Socratic scholar Eduard Zeller has argued that Heraclitus believed that heat in general and dry exhalation in particular, rather than visible fire, was the arche.[48]

In one fragment, Heraclitus writes:

"This world-order [Kosmos], the same of all, no god nor man did create, but it ever was and is and will be: ever-living fire, kindling in measures and being quenched in measures."[bb]

This is the oldest extant quote using kosmos, or order, to mean the world.[1] Fire is the one thing eternal in the universe.[49] From fire all things originate and all things return again in a process of never-ending cycles. He describes the transformations:

"Fire lives the death of earth, and air lives the death of fire; water lives the death of air, and earth that of water."[bc] and "The turnings of fire: first sea, and of sea half is earth, half fireburst. [Earth] is liquefied as sea and measured into the same proportion as it had before it became earth."[bd]

On one interpretation, rejecting both the flux and stability interpretation, Heraclitus is not a material monist, but a revolutionary process philosopher who chooses fire in an attempt to say there is no arche. Fire is a symbol or metaphor for change, rather than the basic stuff which changes the most.[29]Perspectives of this sort emphasize his statements on change such as "The way up is the way down",[w] as well as the quote "All things are an exchange for Fire, and Fire for all things, even as wares for gold and gold for wares",[be] which has been understood as stating that while all can be transformed into fire, not everything comes from fire, just as not everything comes from gold.[29]