Anaximander introduced the concept of the apeiron, meaning the “boundless” or “infinite,” as an underlying principle that explains the origin and nature of everything. Instead of attributing the cosmos to a well-defined element like water or fire, he proposed that the fundamental substance is limitless and indefinable. From this infinite source, all things arise and to it, they eventually return, representing a cycle of creation and destruction. This idea paved the way for thinking about the universe in terms of dynamic and rational processes rather than mythological constructs.