Pausanias Description of Greece 3.4.7

[7]
  Cleomenes had no male issue, and the kingdom devolved on Leonidas, son of Anaxandrides and full brother of Dorieus. At this time Xerxes led his host against Greece , and Leonidas with three hundred Lacedaemonians met him at Thermopylae . Now although the Greeks have waged many wars, and so have foreigners among themselves, yet there are but few that have been made more illustrious by the exceptional valor of one man, in the way that Achilles shed luster on the Trojan war and Miltiades on the engagement at Marathon. But in truth the success of Leonidas surpassed, in my opinion, all later as well as all previous achievements.

[7] Kleomenes had no male issue, and the kingdom devolved on Leonidas, son of Anaxandrides and full brother of Dorieus. At this time Xerxes led his host against Greece, and Leonidas with three hundred Lacedaemonians met him at Thermopylae. Now although the Greeks have waged many wars, and so have barbarians among themselves, yet there are but few that have been made more illustrious by the exceptional valor of one man, in the way that Achilles shed luster on the Trojan war and Miltiades on the engagement at Marathon. But in truth the success of Leonidas surpassed, in my opinion, all later as well as all previous achievements.