The main RuneScape Wiki has an article on: Rune Square Shield
The Old School RuneScape Wiki also has an article on Rune Square Shield.

The Rune Square Shield is a shield which may be equipped by players with level 40 Defense. It requires level 93 Smithing to make from two runite bars, yielding 150 experience. It is the 3rd strongest shield in RSC behind the dragon square shield and the rune kite shield.

Bonuses

Dropped by

Monster Combat level Quantity Rarity
Fire Giant 109 1 4Rare
Black Demon 156, 175 1 4Rare
Black Dragon 200 1 4Rare
King Black Dragon 245 1 4Rare

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