The Sainte-Chapelle (English: Holy Chapel) is a royal medieval Gothic chapel located on the Île de la Cité in the center of Paris. For centuries, the Parisian Brotherhood of Assassins had their headquarters underneath the chapel.
The chapel windows took up all the space between the structural supports, meaning that the stonework was seemingly invisible. The chapel stands out for being completed in 1248, meaning a relatively short construction period. It was set on two levels; the lower level was for Parisians and people of the court, while the upper level was for the king and his family. The crown of thorns was kept in a reliquary to which only the king held the key. On important occasions, he would present the crown to a kneeling congregation.
From around the late 12th century, the Parisian Brotherhood of Assassins began using a cave underneath what would become the Saint-Chapelle as their headquarters. A mechanism on the second floor of the chapel directed sunlight, and when an Assassin medallion was placed in it, the chandeliers would rearrange, allowing the Assassin to reach a beam. Once there, a hole would open in the floor beneath, and the Assassin could perform a Leap of Faith into the sanctuary below.
The sanctuary connected to a series of tunnels beneath Paris, which allowed the Brotherhood to easily navigate the city. Around 1759, a passage was also built between the sanctuary and the Café Théâtre, a business front for the Assassins. In July 1789, Arno Dorian was able to enter the Assassin sanctuary after being given an Assassin medallion by Pierre Bellec, joining the Brotherhood afterwards. In April 1791, he discovered that Bellec had murdered the Mentor Honoré Mirabeau. A swordfight ensued between the two Assassins at the chapel, during which the building's large rosary window was shattered, and Bellec was killed. He would later be buried in the upper chapel of the Sainte-Chapelle.
During the French Revolution, Templar agents stole several priceless relics from the chapel, intending to use the threat of their destruction to blackmail their way into more power. However, a team of Assassins were able to tail the Templars, knock them out and recover the relics. During this period, the chapel also came close to being demolished, but would eventually see use as a flour store, a club room for the revolutionary part of Paris and finally a store for archiving old papers. Since this served the populace, the chapel was spared destruction. Until 1837, it bore a sign saying "National property, for sale". By this point, all the sacred vessels and precious books had long since disappeared.