A series of semi−circular arches is thrown across the angles of the apartment, each projecting further into it than the preceding, and in this way the corners are got rid of, and the square converted into the circular shape. A cornice ran round the apartment, either above or below the pendentives, or sometimes both above and below. The domes were pierced by a number of small holes, which admitted some light, and the upper part of the walls between the pendentives was also pierced by windows.