Before there was a religion called Buddhism, there was, by tradition, a single afternoon in a deer park outside the city of Varanasi. Siddhartha Gautama, newly awakened, sought out five ascetics who had once been his companions and had abandoned him when he chose a middle path between indulgence and extreme self denial. He sat with them and spoke.
What he said became known, in later memory, as the Dhammacakkappavattana Sutta, the discourse on setting the wheel of the dharma in motion. Its content was not elaborate: the four truths of suffering, its cause, its ending, and the path that leads there, stated plainly rather than argued at length across many pages. Its importance lay elsewhere, in the fact that a teaching once held privately by one awakened man now existed spoken aloud between human beings, available to anyone willing to sit and listen.
Every later image of a Buddha in the teaching gesture, hand raised, fingers arranged as though turning something, descends from this remembered afternoon. The wheel became dharma's own emblem because a wheel keeps moving. The point was never a fixed set of rules handed down once and sealed. It was a teaching set turning, meant to keep passing from one generation of listeners to the next exactly as it first passed from five ascetics who had almost given up on their teacher.