Ankh

"If we talk about Egyptian Mythologogy, the Ankh is an artifact of Isis. The Great Goddess. Protector of the Egyptian Empire.... This cross is like a key which allowed a Trayeler to pass through the Gates of Eternity..."

- Lucius talking about the Ankh to his son. The Ankh was a Piece of Eden, capable of temporarily resurrecting the dead.

History
At one point, at the Assassin Lucius' request, the Ankh came into the hands of the his nephew Accipiter, an Alaman. He then passed it on to Lucius' son Aquilus, who brought it back home to his father. Lucius locked it in a box, but the very same day, Lucius was killed by his associate and secret Templar Caius Fulvus Vultur, who took the Ankh from the box.

Trivia

 * The Ankh, also known as the Key of Life or Crux Ansata, was the ancient Egyptian hieroglyphic character which meant "eternal life". It was often worn by Egyptian gods and pharaohs.

Source

 * Assassin's Creed (French comic): Tome 2, Aquilus.