History of the Peloponnesian War

After dinner Demosthenes and the rest of the army set out immediately after nightfall, he himself with half of them making for the pass, while the rest took the road through the Amphilochian mountains.

And at dawn he fell upon the Ambraciots, who were still in their beds and had no knowledge at all of what had previously happened.

On the contrary, they supposed these troops to be their own men, for Demosthenes had purposely put the Messenians in front and directed them to accost the enemy in the Doric dialect, thus getting themselves trusted by the outposts; besides, they were indistinguishable to the sight, since it was still dark. So they fell upon the army of the Ambraciots and put them to rout, slaying the majority of them on the spot;

the rest took to flight over the mountains.