The boyaux are trenches run in a zigzag direction along the capitals of the front of attack, and are intended exclusively for the circulation of the troops; they have no banquettes.

The first parallel is about six hundred yards from the place, and consequently beyond the reach of grape.

It is constructed by the _simple sap_.

After the first night, the guards, instead of advancing in front of the work, are placed in the trenches.
The second parallel (B) is made some three hundred or three hundred and fifty yards from the place, and being much exposed to grape, the _flying-sap_ is employed in its construction.

Batteries (H) are established between the first and second parallels to silence the fire of the demi-lunes of the collateral bastions, and others (I) near the second parallel, to enfilade the faces of the front of attack.