Arrow of iron.
III Iron Arrow is a low-ranked arrow that provides 12 Attack (17 in the NES version). It can be bought for 8 gil at Canaan, Dwarven Hollows, and Amur (all remake only), or found as treasure at Canaan in Cid's basement.
IV Iron Arrow is one of the weakest arrows providing 5 Attack, being only slightly stronger than the Medusa Arrows, and is a Metallic weapon. It can be bought for 10 gil at Kaipo and Agart or found as treasure in Damcyan. Rosa also starts with Iron Arrows when recruited.