The Galerie des Moulages (cast collection) not only contains 19th plaster casts, but also scale models of buildings done by artisans on staff at the museum. Sens Cathedral was one of the earliest Gothic buildings in the country, and the largest of the early Gothic churches. The choir was begun in 1140. As was typical in cathedral construction work progressed westwards, building the nave, with the west front completed around 1200. The structure was finally completed in the 16th century. The main elevation of Sens consisted of three storeys, the arcades and triforium of which remain intact. The clerestory was enlarged in the 13th century by extending the double window openings upward.