Crystal Cube

A Crystal Cube is an object regarded by the Templars during the Renaissance as critical to their order's future. As its name suggests, its form took the shape of a perfect cube.

History
Around 1506 in Rome, in the immediate aftermath of the assassination of Sirus Favero, the Master of the Crows, the Assassins Lo Sparviero and Niccolò Machiavelli hurried to the Crows' hideout to search it for secrets before it could be destroyed. Alongside a chest with a small shard, they were able to recover a painting of the Crystal Cube—referenced in several letters between Sirus and Cesare Borgia—that was hanging from the tip of a Corvix Blade that pinned an eagle carcass to the wall. The painting itself contained a map of Forlì with mysterious markings.

Reference

 * Assassin's Creed: Identity