The Ambraciots made a trench and arranged a row of very thin bronze vessels along its walls. These vessels vibrated to the sound of the digging Romans, so the defenders were able to locate the direction of the enemy tunnel and hit it with their own. At first the two sides fought underground with swords and spears but soon the Ambraciots decided to employ a different method. They put in front of them an earthenware jar made to the width of the mine and bore a hole in its bottom. Then, they filled it with fine feathers and set it on fire, using bellows attached to the hole to fan the flames. The smoke was voluminous and pungent and forced the Romans to retreat.