History of the Peloponnesian War

An unpretentious costume after the present fashion was first adopted by the Lacedaemonians, and in general their wealthier men took up a style of living that brought them as far as possible into equality with the masses.

And they were the first to bare their bodies and, after stripping openly, to anoint themselves with oil when they engaged in athletic exercise; for in early times, even in the Olympic games, the athletes wore girdles about their loins in the contests, and it is not many years since the practice has ceased. Indeed, even now among some of the Barbarians, especially those of Asia, where prizes for wrestling and boxing are offered, the contestants wear loin-cloths.

And one could show that the early Hellenes had many other customs similar to those of the Barbarians of the present day.