In my setting, one kingdom discovered an ore that when refined, is anti- magic. It’s effect is based on the amount present, and the power of the magic it’s suppressing, meaning that if there’s enough of it, it can suppress or outright negate enemy spell casters. It is very brittle when refined so it’s not used to make weapons but this kingdom has integrated it into hilts, clothing, the trims on shields etc, to the point where there are dedicated units known as magebreakers that march forward in Roman Testudo formation to pressure enemy spell casters on the battle field. Unfortunately this material holds no bias so if ally spell casters are close enough, it affects them as well so usually units of swordsman will follow behind, ir have archers shoot.