Apollo Belvedere

For three centuries after its rediscovery around 1489, this was considered the greatest sculpture in the world — the yardstick for classical perfection. Winckelmann wrote pages of ecstatic prose about it. The god has just released an arrow (perhaps at the Python); his weight shifts elegantly onto his right leg in a perfect contrapposto. It's actually a Roman marble copy of a lost Greek bronze, but its influence — on Neoclassicism, on academic drawing, on our idea of what a god looks like — is total.