The gargoyles, which were added to Notre-Dame in about 1240, had a more practical purpose. They were the rain spouts of the church, designed to divide the torrent of water which poured from the roof after rain, and to project it outwards as far as possible from the buttresses and the walls and windows so that it would not erode the mortar binding the stone. To produce many thin streams rather than a torrent of water, a large number of gargoyles were used, so they were also designed to be a decorative element of the architecture. The rainwater ran from the roof into lead gutters, then down channels on the flying buttresses, then along a channel cut in the back of the gargoyle and out of the mouth away from the church.