An improved version of the fortify spell, entrench has much the same effect, but prepares an even more formidable set of defenses. Like fortify, entrench may be used to prepare an open outdoors area such as a field or grassland, or a rough outdoors area such as a hillside or forest. Large rooms or chambers may be entrenched as well. In addition to the ditches and ramparts of the fortify spell, entrench makes use of local materials to create a small palisade and an array of stakes or sharp stones to discourage attackers.
A. Open Outdoors Site: A rampart or dike of earth faced by a staked ditch rises from the ground along the perimeter of the site. Creatures defending the dike receive 75% cover against missile fire (+7 bonus to AC), or 25% cover (+2 bonus) if they expose themselves by engaging in melee combat or firing missiles out of the dike. Attackers cannot charge, run, or sprint over the rampart, and must spend one full round negotiating the defenses in order to attack. The dike's defenders receive a +1 bonus to attack rolls against any creatures trying to move through the stakes or stones.
B. Rough Outdoors Site: Loose stones, deadwood, and briars are arranged to form a defensible wall along the perimeter of the area of effect, faced by an array of sharp stakes or stones. Characters hiding behind the wall receive 90% cover (+10 bonus to AC), or 50% cover (+4 bonus) if they expose themselves by firing missiles or defending the wall. Attacking creatures cannot run, charge, or sprint through the defenses, and must spend one full round to get through the stakes plus an additional round climbing over the wall in order to enter the fortified area. The wall's defenders gain a +1 bonus to attacks against creatures negotiating the defenses.
C. Marshy or Low-lying Site: In swamps or bogs, entrench creates a water-filled ditch around the perimeter of the area of effect. This ditch is 15 feet wide and 3 to 6 feet deep; most creatures require two full rounds to negotiate the ditch and climb up the far side, and defenders gain a +1 bonus to attack rolls against enemies who are wading the ditch or climbing up the other side.
The fortifications created by this spell are permanent, although erosion, weathering, and clearing or filling can return the site to its original state. The material component is the shell of a giant nautilus. In the Battlesystem rules, entrench provides the defending units with a +3 bonus to their AR versus missile and melee attacks, but only a +1 bonus against missile attacks in marshy areas.