The light-drenched domus vitrea (literally "a house of glass") fulfilled Pius’s notion that the structure should symbolize enlightenment. The exterior represents Renaissance ideals of unity with a facade of three blind arches, atop which the pope rather immodestly placed his coat of arms. The light-drenched interior was in part inspired by the pope’s travels in Germany, where he admired hall churches lit by tall windows. For all of its perfection, the structure showed signs of a serious flaw almost as soon as it was completed—the hillside on which it is built is unstable, and the foundations are slowly shifting (as you walk toward the rear, you’ll notice the floor slightly slopes).