Fortifications can be raised or lowered, manned or unmanned. When lowered they will not block the passage of troops but will strike back against besieging with albeit with reduced potency. When raised, ALL passage of legions will be blocked and the forts will fight back with greater strike power when besieged. Manned fortifications have much enhanced offensive capability - meaning more damage is done to legions laying siege / within range.
Fortifications need to be manned by a legion of company or above size to allow the RAISE or LOWER commands to be used. It is not possible to raise or lower forts when unmanned and, even if raised, the strike power against invaders is a fraction of the potency when manned by defender legion(s).
TO RAISE OR LOWER FORTIFICATIONS
Lowered forts are mostly useless. Raised forts are peace of mind, protecting your territory or your homeland from invasion. It is a good rule of thumb that 100,000 fortification potency on your home city gates equates to 24 RL hours protection. They exist to ensure no surprise attack can penetrate a city's precious interior even if launched deliberately when the high command is abed!
Syntax: COM FORTIFY RAISE/LOWER.
Fortifications must be manned to be raised or lowered and the speed of the raising/lowering depends on the numbers available for the task - the legionnaires manning and unoccupied with some other task or combat or other distraction.
NOTE: Raising and lowering fortifications not of your own creation (e.g. when abroad, fortifying your sphere of influence) requires your legions to be on homeland soil, or in a location part of conquered territory.
TO MAN FORTIFICATIONS
Syntax: COM STEP <direction> to be adjacent to forts.
Move your legion into position so it is in the same point as the fortifications you wish to man.
Syntax: COM FACE <direction of forts to be manned>.
Make sure the legion is facing a useful direction for future raising and/or lowering of forts.
Syntax: COM DEPLOY FORTS <percentage of legion>.
You can have your legions man fortifications of their own homeland or in locations part of their sphere of influence (i..e. where the flag of the homeland has been raised). You will need to have sufficient of your legion allocated to "forts" skill, and ????ACTIVITY covering a high enough percentage to include those you allocate to "forts". This will determine the speed and volume of legionnaires moved per round into the fortifications. To unman you simply need remove the forts percentage (set it to zero) and then wait while the legionnaires disengage themselves from the forts.
While manning fortifications, legionnaires within are not susceptible to attack by any means save the pouring of oil from an oil-cauldron (see HELP OILCAULDRON for specifics), nor are they able to launch attacks against opposing forces from this protected position. Fortifications can hold, at most, 10% of their defensive potency in legionnaires manning. Therefore a fortification of 10000 strength can accomodate a maximum of 1000 legionnaires deployed about the fort-manning task.
NOTE: If a legion's numbers exceed the maximum that can be safely deployed into fort-manning, the excess troops are NOT protected and are free to attack and be counter-attacked by any other legions on the battlefield.
Laying siege to fortifications and indeed besieging generally, in addition to further information about fortification defensive-work can be found in HELP BATTLEFIELD, while construction is further documented in HELP EQUIPMENT.