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

An Iron Square Shield is a shield which can be equipped from level 1 defense onwards. It requires level 23 smithing to make this item from two iron bars, resulting in 50 smithing experience. It can also be bought from Cassie's Shields for 168 coins.