History of the Peloponnesian War

Having thus spoken, and dismissed the assembly, Archidamus first sent Melesippus son of Diacritus, a Spartan, to Athens; in case the Athenians might be more disposed to submit, when they saw that the Peloponnesians were now on their march. But they did not admit him into the city, nor to their assembly;

for the opinion of Pericles had previously been adopted, not to admit any herald with an embassy from the Lacedaemonians, when they had once marched out from their frontiers. They sent him back therefore before hearing him, and ordered him to beyond the borders that same day, and [to tell those who sent him] that in future, if they wished to propose any thing, they should send ambassadors after they had retired to their own territories.

And they sent an escort with Melesippus, to prevent his holding communication with any one. When he was on the frontiers, and was about to be dismissed, he spoke these words and departed

This day will be the beginning of great evils to Greece.

When he arrived at the camp, and Archidamus found that the Athenians would not yet submit at all, he then set out and advanced with his army into their territory.

At the same time, the Boeotians, while they furnished their contingent and their cavalry to join the Peloponnesians in their expedition, went to Plataea with the remainder of their force, and laid waste their land.