backside of the Notre Dame Cathedral, Paris, France. .... Maurice de Sully, bishop of Paris, decided to build a new cathedral for the expanding population, dedicated to the Virgin Mary. Although construction started in 1163, it was not completed until roughly 180 years later in about 1345. Built in an age of illiteracy, the cathedral retells the stories of the Bible in its portals, paintings, and stained glass. On completion of the choir in 1183, work was begun on the nave and completed c.1208, followed by the west front and towers c.1225-1250. A series of chapels were added to the nave during the period 1235-50, and to the apse during 1296-1330 (Pierre de Chelles and Jean Ravy). Transept crossings were built in 1250-67 by Jean de Chelles and Pierre de Montreuil (also the architect of the Sainte-Chapelle). The six-part rib vaults and the thin elements articulating the wall are typically Early Gothic.