Heraclitus (; Greek: Ἡράκλειτος Herákleitos; fl. c. 500 BC) was an ancient Greek pre-Socratic philosopher from the city of Ephesus, which was then part of the Persian Empire. Little is known of Heraclitus's life. He wrote a single work, only fragments of which have survived. Most of the ancient stories about him are thought to be later fabrications based on interpretations of the preserved fragments. His paradoxical philosophy and appreciation for wordplay and cryptic, oracular epigrams has earned him the epithets "the dark" and "the obscure" since antiquity. He was considered arrogant and depressed, a misanthrope who was subject to melancholia. Consequently, he became known as "the weeping philosopher" in contrast to the ancient philosopher Democritus, who was known as "the laughing philosopher". The central idea of Heraclitus' philosophy is the unity of opposites and the concept of change. He also saw harmony and justice in strife. He viewed the world as constantly in flux, always "becoming" but never "being". He expressed this in sayings like panta rhei ("Everything flows") and "No man ever steps in the same river twice." This changing aspect of his philosophy is contrasted with that of the ancient philosopher Parmenides, who believed in "being" and in the static nature of reality. Like the Milesians before him, Thales with water, Anaximander with apeiron, and Anaximenes with air, Heraclitus chose fire as the arche, the fundamental element that gave rise to the other elements. He also saw the logos as giving structure to the world. Source: Wikipedia (en)