This was soon accomplished, for the Romans had not only brought their mine up to the wall, but had under-pinned a considerable length of it on either side of their mine and thus the two parties found themselves face to face. Having marked the spot indicated by any of these brazen vessels, which were extraordinarily sensitive and vibrated to the sound outside, they began digging from within, at right angles to the trench, another tunnel leading under the wall, so calculated as to exactly hit the enemy's tunnel. When the trench was made to the required depth, they next placed in a row along the side of the trench nearest the wall a number of brazen vessels made very thin and, as they walked along the bottom of the trench past these, they listened for the noise of the digging outside. For a considerable number of days the besieged did not discover them carrying the earth away through the shaft but when the heap of earth thus brought out became too high to be concealed from those inside the city, the commanders of the besieged garrison set to work vigorously digging a trench inside, parallel to the wall and to the stoa which faced the towers. Having safely secured the central one of their three works, and carefully concealed the shaft with wattle screens, they erected in front of it a covered walk or stoa about two hundred feet long, parallel with the wall and beginning digging from that, they carried it on unceasingly day and night, working in relays. offered a gallant resistance to the assault of the siege artillery and, therefore, in despair had recourse to mines and tunnels. The Greek historian Polybius, in his Histories, gives a graphic account of mining and counter mining at the Roman siege of Ambracia: They can be part of an extensive labyrinth and have culs-de-sac and reduced lighting, typically creating a closed-in night combat environment. Tunnels are narrow and restrict fields of fire thus, troops in a tunnel usually have only a few areas exposed to fire or sight at any one time. A good example of this was seen in the Syrian Civil War in Aleppo, where in March 2015 rebels planted a large amount of explosives under the Syrian Air Force Intelligence Directorate headquarters. Since tunnels are commonplace in urban areas, tunnel warfare is often a feature, though usually a minor one, of urban warfare. Defenders have dug counter-mines to attack miners or destroy a mine threatening their fortifications. Since antiquity, sappers have used mining against walled cites, fortresses, castles or other strongly held and fortified military positions. Also, tunnels can serve as shelter from enemy attack. Tunnels can be used to undermine fortifications and slip into enemy territory for a surprise attack, while it can strengthen a defense by creating the possibility of ambush, counterattack and the ability to transfer troops from one portion of the battleground to another unseen and protected.

It often includes the construction of underground facilities (mining or undermining) in order to attack or defend, and the use of existing natural caves and artificial underground facilities for military purposes. Tunnel warfare involves war being conducted in tunnels and other underground cavities.

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