History of the Peloponnesian War

And it is said that the motive of Archidamus in waiting about Acharnae with his troops ready for battle, instead of descending into the plain during this invasion, was as follows:

He cherished the hope that the Athenians, who were at their very best as regards the multitude of their youth and prepared for war as never before, would perhaps come out against him and not look on and see their land ravaged.

So when they did not come to meet him at Eleusis and in the Thriasian plain, he settled down in the neighbourhood of Acharnae, to make a test whether they would come out;

for not only did that seem to him a suitable place for his camp, but also the Acharnians were an important part of the state, their hoplites numbering three thousand, and he thought that they would not look on and see their fields ravaged, but would urge the whole people also to fight. And even if the Athenians should not come out against him during this invasion, he would thenceforward proceed with less apprehension to ravage the plain and even advance to the very walls of the city; for the Acharnians, once stripped of their own possessions, would not be as eager to incur danger as before in behalf of the lands of the rest, and so a division would arise in the counsels of the Athenians.

It was with this design that Archidamus stayed at Acharnae.