Diodorus' Account of Thermopylae
Diodorus' account of the Battle of Thermopylae (480 B.C.) in the Persian Wars is different from that of Herodotus. Diodorus says the men under Leonidas, most of whom had previously undergone the Spartan krypteia, attacked the enemy under cover of nightfall, preventing the Persians from knowing how small their number was. A side result was that in the confusion, Persians killed each other. Herodotus describes the events differently and says the battle was by day.
"Leonidas was warned by a Ceymean named Tyrrhastiades... who deserted from the Persian camp, that an enemy force was soon to appear in his rear. Leonidas then led a valiant night attack on the Persian camp and even came close to killing Xerxes himself in the royal tent. Indeed, if Xerxes had been found in his tent, 'the whole war would have reached a speedy conclusion' (11.10.3)."
This night attack may have been an invention, or it could contain some truth, but Justin in his Epitome of Pompeius Trogus (2.11.12-18) and Plutarch (whose source may also have been Ephorus or the poet Simonides, whom Diodorus quotes) in his On the Malice of Herodotus 866a also mention the night attack.
Justin - Epitome of the Philippic History of Pompeius Trogus Book II
At the beginning of the war, when the Spartans consulted the oracle at Delphi, they had received the answer, that "either the king or their city must fall." King Leonidas, accordingly, when he proceeded to battle, had so fixed the resolution of his men, that they felt they must go to the field with minds prepared for death. He had posted himself in a narrow pass, too, that he might either conquer more gloriously with a few, or fall with less damage to his country. The allies being therefore sent away, he exhorted his Spartans "to remember that, however they struggled, they must expect to perish; to take care not to show more resolution to stay than to fight;" adding that, "they must not wait till they were surrounded by the enemy, but when night afforded them opportunity, must surprise them in security and at their ease; as conquerors could die nowhere more honourably than in the camp of the foe." There was no difficulty in stimulating men determined to die. They immediately seized their arms, and six hundred men rushed into the camp of five hundred thousand, making directly for the king's tent, and resolving either to die with him, or, if they should be overpowered, at least in his quarters. An alarm spread through the whole Persian army. The Spartans being unable to find the king, marched uncontrolled through the whole camp, killing and overthrowing all that stood in their way, like men who knew that they fought, not with the hope of victory, but to avenge their own deaths. The contest was protracted from the beginning of the night through the greater part of the following day. At last, not conquered, but exhausted with conquering, they fell amidst vast heaps of slaughtered enemies. Xerxes, having thus met with two defeats by land, resolved next to try his fortune by sea.
(From On the Malice of Herodotus)Next: Where Diodorus May Be More Accurate than Herodotus
Now Herodotus, in his narration of that fight, hath obscured also the bravest act of Leonidas, saying that they all fell in the straits near the hill. (Herodotus, vii. 225.) But the affair was otherwise managed. For when they perceived by night that they were encompassed by the barbarians, they marched straight to the enemies' camp, and got very near the King's pavilion, with a resolution to kill him and leave their lives about him.