Grand Temple Key

The Grand Temple Key was an amulet-like Piece of Eden that functioned as a key to unlock the gate inside the Grand Temple in.

In 1754, the key was in the possession of an elderly member of the Assassin Order. On orders of Grand Master Reginald Birch, Haytham Kenway assassinated the man inside the in London and took the key from him. Upon Haytham's return to the Templar headquarters, Birch told Haytham that the key likely opened a First Civilization storehouse in the New World. Birch booked Haytham passage to Boston to find it and unlock its contents, and to establish a permanent Templar presence in the colonies.

In 1755, Haytham found the Grand Temple, but was unable to access it because he did not possess an Apple of Eden to open the first door. Haytham kept the amulet in his possession until 1781, when he passed it on to his second-in-command Charles Lee.

The Assassin Connor, son of Haytham, killed Charles Lee in 1782 in Boston and took the amulet from him. Connor later returned to his Mohawk village of Kanahséton where he activated his tribe's Crystal Ball he used years earlier to communicate with Juno. Juno greeted Connor again, and told him to hide the amulet where none might find it. Connor made his way back to his home and hid the key in the grave of Connor Davenport, whom Connor's mentor Achilles Davenport named him after.

In 2012, Connor's descendant Desmond Miles relived Connor's memories inside the Animus and found out where the key was hidden. After having retrieved it, Desmond used it to open the gate in the Grand Temple.

Reference

 * Assassin's Creed III