What artifact is the most frequently featured Piece of Eden in Assassin's Creed?

The Apple of Eden is the most frequently featured Piece of Eden in Assassin's Creed.

In the series' mythology, Apples of Eden are powerful Isu artifacts that can influence human minds, create illusions, and project energy. They were created by the Isu, an advanced civilization that existed before recorded human history. Templars and Assassins repeatedly seek them because their abilities could be used to control populations or protect free will.

The Apple appears prominently in the first Assassin's Creed game and returns throughout later entries. Several Apples exist in the fictional universe, so the term does not always identify one single physical object. Other Pieces of Eden include the Staffs, Swords, Shrouds, and Rings of Eden, but the Apple is the artifact most strongly associated with the franchise's recurring plot.