Part 1 deals with the arrival of the Dorian settlers into the Eurotas valley, with a discussion of the dark-age culture that lived there before, that of Menelaus, and his wife Helen (known to history as Helen of Troy). Once established, the Spartans expand westward into Messenia, enslaving the entire population, eventually becoming the dominant power in Laconia. During this time Lycurgus transforms the Spartan constitution into the militarised state we know of today. The training of Spartan youths is explained, from their enrollment in the Agoge system right through to their attainment of citizenship. The class structure of the Lacedaemonian state (Helots, Perioeci, and the soldier-citizens themselves) is also covered. The episode ends with the battle of Thermopylae, in which 300 Spartans, including their king, Leonidas, were killed in action defending Greece from a Persian invasion.