Battle of Thermopylae

King Leonidas and 300 Spartans (plus a few thousand other Greeks everyone forgets about) held the narrow pass at Thermopylae against Xerxes I's massive invasion force for three days in 480 BCE. They all died, but they bought enough time for Greece to organize. The epitaph at the site reads: 'Go tell the Spartans, stranger passing by, that here obedient to their laws we lie.' Hardest thing ever written on a rock, no debate.