Titus Livius (Livy), The History of Rome, Book 38
Evan T. Sage, Ph.D., Ed.

7. When Perseus learned that the Aetolians were approaching, he abandoned the siege of the city he was investing and, merely plundering the fields, withdrew from Amphilochia and returned to Macedonia. [2] The Aetolians too were called away from there by the devastation of their sea-coast. Pleuratus,¹ the king of the Illyrians, sailed into the Corinthian gulf with sixty cruisers and joining the ships of the Achaeans which were at Patrae was laying waste the coast districts of Aetolia. [3] A thousand Aetolians sent against them, wherever the fleet went, following the indentations of the shoreline, would travel by shorter routes and meet them. [4] Also the Romans before Ambracia, by battering at the walls with rams, had to a great extent laid bare the town, but nevertheless could not force their way into it; [5] for with equal speed a new wall was thrown up to replace what had been destroyed and armed men, standing on the ruins, served as a fortification. [6] Accordingly, since visibly applied force was not [p. 23]progressing well for the consul, he determined to dig² secretly a tunnel in a place formerly covered by his sheds, and for a considerable period, although the work was in progress day and night, not only the men digging beneath the ground but also those who were carrying out the earth went unnoticed by the enemy. [7] Suddenly a rising mound of earth betrayed the work to the townspeople, and, fearing that the walls had already been undermined and a way opened into the city, they began to dig a ditch inside the wall in the direction of that work which had been covered by the sheds.³ [8] When they came to a depth as great as the bottom of the tunnel could have, they remained silent, and placing their ears against the walls in several places they listened for the sound of the diggers. [9] When they heard this they opened a way straight into the tunnel, nor was this a difficult task; for in a moment they came into the open space where the enemy was supporting the roof on props. [10] The works joining there, as the way was open from the trench to the tunnel, they began to fight, at first with the same tools which they had used in the work, then quickly armed men too came up and engaged in a hidden battle underground; later this fighting became more desultory, since they blocked the tunnel wherever they wished, now with curtains⁴ stretched across, now with hastily constructed doors.⁵ A new device as well, and one easy of execution, was thought out against the Romans who were in the tunnel. [11] They prepared a cask pierced at the [p. 25]bottom, where a pipe of moderate size could be⁶ inserted, and likewise an iron pipe and an iron lid for the cask, this lid too being perforated in several places. This cask, filled with light feathers, they placed with its mouth facing the tunnel. They fixed in the holes in the lid the very long spears which they call “sarisae,” so as to keep the enemy at a distance. [12] A light spark of flame, placed among the feathers, they fanned by blowing with a smith's bellows placed at the mouth of the pipe. [13] Then, since smoke, not merely abundant in quantity, but, even more, unendurable by reason of the vile stench from the burning feathers, had filled the whole tunnel, scarcely anyone was able to remain within it.⁷