I'm working on a campaign wherein everybody is basically a Roman Legionnaire, so I think I need some more rules for shields and shield use.

1st, since it's a primative campaign (severely cut down weapon use talents, since there aren't any modern weapons) "Shield" is a weapon class, which like all the other weapon use talents allows the use of the shield without penalty.

2nd, I was considering using the Double Team rules as a template for a Shield Wall talent. Basically, keeping it exactly the same, but allowing the bonus only to Parry attempts using the shield.

3rd, I'm planning to make some sort of "shield expert", which would allow a person to attack with a shield without suffering the -20 shield penalty (the -10 defensive penalty would still apply). The other part of the Shield Expert talent would be a shield bash that does no damage, which removes both the atacker and defender's ability to use a shield for the rest of the round (or should this be yet another individual talent.).

4th, are there rules somewhere for using a shield wall for cover or concealment against ranged attacks? I seem to remember seeing something somewhere, but I can't find it now. If no, how should I simulate someone wanting to "parry" arrows with their shields?

Does anyone see any huge problems with these ideas?

Blood of Martyrs has a sacred shield for the Sororitas (Praesidium Protectiva) which works like the following:

• bearer is restricted to one-hand weapons whilst carrying the shield
• bearer may bash with the shield in close combat (does some Impact damage + character's SB)
• bearer may spend a reaction to parry an incoming attack (ranged and melee) using her Weapon Skill
• may only parry attacks coming from the front or the side where the shield is carried
• against melee attacks the parry works like a regular Parry
• against ranged attacks the parry confers a certain amount of bonus AP to the affected body zone's armour

Note that these rules differ a bit from the other shields that are already in the game - for example, the shields in Ascension simply add a couple "passive" AP to the character's torso and shield-arm and forego any of the more "advanced rules" concerning Parry Tests, though they too can be used to bash. That said, the Battle Sisters' shield rules seem to be more comprehensive and are probably what you might be looking for in terms of inspiration.

As for special shield wall rules, how about if you just add +10 to the Parry Test if a character wearing a shield wall has an ally with a shield next to him, and +20 if he is flanked by allies on both sides? Simple and easy.

(edit: though I just noticed that this essentially is just like Double Team, heh)

In case you want to use the "passive AP" solution from Ascension (like, to reduce the need for dice rolls that comes with the more complex Parry rules) I'd just have each flanking shield add 1-2 bonus AP, maybe +2 to the ally's nearby arm (thus "balancing" the lack of his own shield's cover there) and +1 for the ally's torso.

Normally most shields in DH give you additional armor to the arm holding the shield and the body.
Just take that as a basis.

Example:
Shield wall: if standing side by side every shield gives its AP bonus to the weapon arm of the one beside your shild arm in addition to the normal bonuses. For tower shields count the AP bonus to the legs, too.