Erected by Louis IX, this magnificent chapel was originally designed to house precious religious treasures. At the time known as the stairway to heaven, the chapel is one of the masterpieces of medieval architecture.Located on the Île de la Cité, a small island in the center of Paris, the idea for the Sainte-Chapelle (Holy Chapel) originated in 1241 with Louis IX, who was looking for a proper place to house the Crown of Thorns and a fragment of the True Cross, relics from the Passion that he had purchased two years prior from Byzantine Emperor Baldwin II. The king had paid quite a price for these relics, about 135,000 livres, nearly four times what it would cost to build the chapel to display them. More relics were added at later dates.The plans for Sainte-Chapelle are attributed to Pierre de Montreuil, who had also created designs for the Saint-Denis Basilica and part of the Notre-Dame Cathedral. Groundbreaking occurred in 1242 and the chapel was completed in an amazing six years time.