Once upon a time, in the dim recesses of a cave in what is now northern Spain, an artist carefully applied red paint to the cave wall to create a geometric design—a ladder-shaped symbol composed of vertical and horizontal lines. In another cave hundreds of kilometers to the southwest another artist pressed a hand to the wall and blew red paint around the fingers to create a stenciled handprint, working by the flickering firelight of a torch or oil lamp in the otherwise pitch darkness. In a third cave, located in the far south, curtainlike calcite formations were decorated in shades of scarlet.