The Head of Saint Denis was an ancient head-shaped lantern, which encased an Apple of Eden. While fueled by the Apple, the artifact emitted a shimmering blue light and possessed the power to project illusions, as well as imbue weapons with a mystical power. Following the Apple's removal, the Head of Saint Denis became a regular, but self-luminating lantern, requiring no fuel.
In August 1794, Arno Dorian battled a group of tomb raiders sent by Napoleon Bonaparte in order to find the artifact in the First Civilization Temple hidden beneath the Basilica of Saint-Denis. The Assassin killed their leader, Philippe Rose, and used the power of the Apple contained within the lantern to repel the remaining raiders.
Realizing the dangers of the lantern should it fall into Napoleon's hands, Arno removed the Apple stored within and contacted the members of the French Assassin Brotherhood, asking them to send the Apple to Al Mualim in Cairo. Upon delivering the artifact to its escort, Arno kept the Head of Saint Denis itself as a memento.
By 1868, the lantern had been obtained by the British Rite of the Templar Order, and was kept by David Brewster inside his laboratory. It was destroyed alongside the laboratory when the device he used to experiment on an Apple of Eden malfunctioned, causing the Piece of Eden to detonate.