History of the Peloponnesian War

Meanwhile the troops from the city of Ambracia arrived at Idomene. Now it consists of two lofty hills, and of these the higher had already been seized unobserved during the night by the troops which Demosthenes had sent forward from his main army; but the lower had previously, as it chanced, been ascended by the Ambraciots, who spent the night there.

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;