Château de Saint-Germain-en-Laye

The Château de Saint-Germain-en-Laye (French pronunciation: ​[ʃɑto də sɛ̃ ʒɛʁmɛ̃ ɑ̃ lɛ]) is a royal palace in the commune of Saint-Germain-en-Laye, in the département of Yvelines, about 19 km west of Paris, France. Today, it houses the Musée d'Archéologie Nationale (National Museum of Archaeology).

The first castle, named the Grand Châtelet, was built on the site by Louis VI in around 1122. The castle was expanded by Louis IX of France in the 1230s.

Louis IX's chapelle Saint Louis at the castle belongs to the Rayonnant phase of French Gothic architecture. A 1238 charter of Louis IX instituting a regular religious service at the chapel that we first learn of a chapel having been built at the royal castle. This was a Sainte Chapelle, to house a relic of the Crown of Thorns or the True Cross. Its plan and architecture prefigure the major Sainte-Chapelle which Saint Louis built within the Palais de la Cité at Paris between 1240 and 1248. Both buildings were built by Louis's favourite architect Pierre de Montreuil, who adapted the architectural formulae invented at Saint Germain for use in Paris. A single nave ends in a chevet, with almost all the wall areas filled by tall thin glass windows, between which are large exterior buttresses. The ogives of the vault rest on columns between the bays and the column bases are placed behind a low isolated arcade. The building can thus be open and empty of all internal supports. This large number of windows is also enabled by the pierre armée technique, with metal elements built into the structure of the walls to ensure the stones' stability. The west wall is adorned by a large Gothic rose window in the "rayonnant" Gothic style. It was in this chapel in 1238 that Baldwin II of Constantinople presented Louis with the relic of the crown of thorns and, though they were intended for the Sainte-Chapelle in Paris, they were housed here until the Paris chapel was consecrated in April 1248.

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