These are armed in part with mortars and in part with heavy siege-pieces.
The works are now gradually pushed forward to the third parallel, (C), which is constructed about sixty yards from the salients of the place.
As the operations of the besiegers are here greatly exposed to musketry fire, the trenches are constructed by the _full-sap_.

The third parallel, having to contain the guards of the trenches, and being of less development than the two preceding, is made much wider.

The second parallel now contains the reserve, and the first parallel becomes the depot of materials.

_Demi-parallels_ (G) are frequently established between the second and third, to be occupied by detachments of guards.
The operations of defence during this period are so directed as to harass the workmen in the trenches and retard the advance of the works of attack.

Garrison pieces of long range and large howitzers are brought forward on the salients of the bastions and demi-lunes of attack, so as to fire in ricochet along the capitals on which the boyaux must be pushed: light and fire-balls are thrown out as soon as it becomes dark, to light up the ground occupied by the besiegers, thus exposing them to the fire of the work and to the attacks of the sortie parties.