Forts

[Tiberius Nero]

The only use of forts in RTW is to guard narrow mountain passes, with just one cheap unit as garrison (if it is a depleted unit of 2 soldiers you wont bother to retrain, its ideal). When the fort gets besieged, move a real army to attack the besiegers. Having a large force of your own caught in a siege inside a fort is more of a trouble for you than the attacker, because the only thing to do is sally and you will have to organize your army just in front of an already organized one, which is likely to attack you as you deploy.

Even if you end up defending against an attack to the fort (which is unlikely, since tha AI always wastes a turn when besieging, builds equipment on the second and attacks on the third, if it has enough equipment, and a fort can only withstand 3 turns of siege), even then you are at a disadvantage as opposed to an open field battle, as siege battles are brutal for both sides, little maneuvering is allowed in the bugged alleys of forts and it practically boils down to man-to-man combat, with little flanking. Cavalry is also useless in fort battles.

Just my tuppence.

P.S. just play with time limit, there is really no reason not to; if a battle takes more than the time limit it is more likely that something has gone wrong, like you having basically won and being unable to catch that skirmisher cavalry unit which just won't sit still, or that the AI decides not to attack the walls or sally after all, and similar stuff.