The most striking thing is its black colour, which is due to the Volvic lava rock used to build it. Construction began in 1248 in a style inspired by the Gothic cathedrals of the Paris region. In 1866, Viollet-le-Duc added the two iconic spires, which herald the city from afar. Note the superb blue- and red-toned stained-glass windows and, in the chancel chapels, one of the most abundant sets of frescoes from the 12C-15C to be conserved in a French cathedral.