The 300 spartans were Hoplites, heavily armed infantry.
"Hoplites wore tunics under other armor that included breastplates, helmets, and greaves. They carried spears and swords to use in their close style of fighting. Spartan hoplites also wore a short red cloak and long hair."
http://ancienthistory.about.com/od/g.../g/Hoplite.htm
Without the shields or armour the greeks would never have survived the initial onslought of arrows. Not widely known is the fact that the 300 spartans were aided by 1000 Thespians (no not actors
) and Thebans who elected to stay and fight...although the Thebans surrendered just before the final slaughter.
The Greek armour/shield and military skill with the spear easily kept the 'Immortals' back as they were lightly armoured and had 'wicker' shields.
The spartans were true warriors....their 7-8 year old sons would be taken away from their families and trained in millitary schools, severe injury and death during training was not uncommon. One test on the young boys was to be publicly flogged until they uttered a sound.....the last boy to cry out was the winner
Even the women were taught how to fight ....with or without weapons
One of the tasks to prove their manhood was to sneak out of the military school ...unseen ...and strangle (to death) a male slave (being a military state much manual labour was done by captured soldiers whom were enslaved) and return...undetected. If caught they were severely punished.