According to the AD&D rules, a heavy ballista firing a 25 lb bolt at 300 miles an hour would do 3d10 hp?!! Ever seen what the Romans' weapons did, or a trebuchet throwing a piano 200 yards? (A guy in England's got a trebuchet in his field!) Light ballistae were capable of firing a bolt 400 yards that could punch through a pallisade wall and kill the poor sod standing behind it, check British archaeolgical studies.

To reflect the deadly nature of seige weapons, their damage should be increased. Their THAC0s should be poor, as they currently are, as training them on a target isn't easy, however, they reduce the target's AC by 10, except for bonuses due to Dexterity, magic or cover, since they can punch through or flatten plate armour.

Note: Catapults can fire single, large rocks that can bounce for some distance and hit numerous folk, while ballistae hurl giant bolts that can plough straight through several humans. Alternatively, both types can be altered (especially catapults) to fire lots of small projectiles that will affect a wide area (shrapnel).