The Horadric Cube is a powerful artifact created by the Horadrim countless years ago. It is used to combine different items into a new object and does this not by simply combining the constituent pieces physically, but rather merges their "Prime Essence". This process will only work with items that "resonate" with each other, occurs wholly within the cube and it is beyond any mortal craftsmen to replicate the results. Another useful aspect of the cube for adventurers is that by some unfathomable enchantments the space contained within the cube is more than that of the cube itself, taking up just four inventory slots while providing twelve.
In Diablo II the cube is found in the Halls of the Dead, Act II, guarded by Bloodwich the Wild. It is useful as a storage device and to combine gems and other items, but is also crucial to the story. In Act II, the player must use the cube to combine the Amulet of the Viper and the Staff of Kings, forming the Horadric Staff which is used to gain access to Tal Rasha's tomb. Then, in Act III, the cube is used again to combine Khalim's eye, brain, heart and flail to form Khalim's Will a unique mace that is used to destroy The Compelling Orb to gain access to Mephisto's Sanctum.
- 3 gems of equal quaility = 1 gem of higher quality
- 3 runes of the same type = 1 higher level rune
- 3 magic rings = 1 magic amulet
- 3 magic amulets = 1 magic ring
- 3 small potions = 1 large potion
- 2 quivers of arrows = 1 quiver of bolts
- 2 quivers of bolts = 1 quiver of arrows
- 1 axe 1 dagger = 1 stack of throwing axes
- 1 quiver of arrows 1 spear = 1 stack of javelins
- 1 healing potion 1 strangling gas potion = 1 antidote potion
- Wirt's Leg 1 tome of town portal = entrance to the Secret Cow Level