History of the Peloponnesian War

The reason why Archidamus remained in order of battle at Acharnae during this incursion, instead of descending into the plain, is said to have been this.

He hoped that the Athenians might possibly be tempted by the multitude of their youth and the unprecedented efficiency of their service to come out to battle and attempt to stop the devastation of their lands.

Accordingly, as they had not met him at Eleusis or the Thriasian plain, he tried if they could be provoked to a sally by the spectacle of a camp at Acharnae.

He thought the place itself a good position for encamping; and it seemed likely that such an important part of the state as the three thousand heavy infantry of the Acharnians would refuse to submit to the ruin of their property, and would force a battle on the rest of the citizens. On the other hand, should the Athenians not take the field during this incursion, he could then fearlessly ravage the plain in future invasions, and extend his advance up to the very walls of Athens. After the Acharnians had lost their own property they would be less willing to risk themselves for that of their neighbors; and so there would be division in the Athenian counsels.

These were the motives of Archidamus for remaining at Acharnae.