While the besiegers are establishing their enfilading batteries, a strong fire of solid shot and shells will be concentrated on the points selected for their construction.

The garrison will also labor during this period to put the work into a complete state of defence: constructing all necessary palisadings, traverses, blindages, barriers; and strengthening, if necessary, the covering of the magazines.
_Third period._--After the completion of the third parallel, the crowning of the covered way may be effected by storm, by regular approaches, or (if the work is secured by defensive mines) by a subterranean warfare.
In the first case stone mortar-batteries are established in front of the third parallel, which, on a given signal, will open their fire in concert with all the enfilading and mortar batteries.

When this fire has produced its effect in clearing the outworks, picked troops will sally forth and carry the covered way with the bayonet, sheltering themselves behind the traverses until the sappers throw up a trench some four or five yards from the crest of the glacis, high enough to protect the troops from the fire of the besieged.

It may afterwards be connected with the third parallel by boyaux.
When the covered way is to be crowned by regular approaches, a _double sap_ is pushed forward from the third parallel to within thirty yards of the salient of the covered way; the trench is then extended some fifteen or twenty yards to the right or left, and the earth thrown up high enough to enable the besiegers to obtain a plunging fire into the covered way, and thus prevent the enemy from occupying it.

This mound of earth is termed a _trench cavalier_, (O).