Crystal Skulls

"The priest pulls out another skull, crystal, and holds it high. The relic! I hear its hum in my own skull. Faint, but familiar!"

- Giovanni Borgia, upon first sighting a Crystal Skull.

The Crystal Skulls were Pieces of Eden created by the First Civilization, and were scattered throughout Central and South America. They mainly came into the possession of Aztec,, and civilizations.

Renaissance
"I hear talking, but I cannot understand the words! I see a face within its cloudy core. No... in my mind. It has appeared in my mind!"

- Giovanni studying the Skull, 1542.

In 1520, one Skull was located by Giovanni Borgia, an Assassin who had been sent to become a member of Hernán Cortés' crew, in order to search for Pieces of Eden. He managed to intercept one from an Aztec priest in Tenochtitlan, where it was being used as part of a human sacrifice ritual.

Upon returning to Europe, Giovanni took it to the scientist Bombastus, who was an expert in studying the Pieces of Eden. Though he subjected it to several tests, Bombastus was unable to discover its purpose, and the Brotherhood dismissed the Skull as little more than an ornate treasure.

Despite this, Giovanni continued to study the Skull, gazing into it for at least an hour each day for about 22 years. Finally, in 1542, an unknown Chinese man, who had apparently also acquired a Skull, used its communicative powers to contact Giovanni.

Modern times
"The good news is that they work. As a result, we now have a safe and secure communication channel for use after the launch."

- Alan Rikkin reporting on the Skulls.

As of 2012, a number of the Skulls had come into the possession of Abstergo Industries. Alan Rikkin noted in an email to Warren Vidic that the "" worked, but were extremely few in number.

The Templars planned to use them as a completely secure means of communication, which the modern-day Assassins would be unable to trace. Due to their limited number, only the most essential facilities or members (including Warren Vidic) would have access to the Skulls.

Trivia

 * A message that Clay Kaczmarek wrote stated that "Within Emperor Jiajing's sin and Quetzalcoatl's hunger lies the answers." The Chinese man who contacted Giovanni could presumably have been Emperor Jiajing, a Templar-aided Chinese emperor, who hunted the Chinese Assassins. is a reference to the Mesoamerican deity, which would tie to the Mitchell-Hedges Skull.