The first significant Gothic landmark was the ambulatory of the abbey of Saint-Denis in France. It embodied the first daring use of large areas of glass. It influenced the cathedrals of Sens, Noyon, Laon, and Paris. In the later years of the period, further reduction of opaque wall surfaces in favor of screens of stone tracery and glass emerged, forming the Gothic Rayonnant style, characterized by walls made almost entirely of glass, supported by a thin skeletal frame of masonry. Limestone was the main building material used in France as it was soft to cut, but gets harder when the air and rain get on it. Limestone gives a pale gray color and it is perfect for making very fine carvings. French cathedrals were often very high, both inside and outside, with the facades having three doors, a rose window, and two towers.