Bernini also designed the altar in the chapel. The design of the altar is based on two curves. Overall, it is bowed (convex), but the backdrop to the sculptural group is coved (concave). The altar is fabricated from polychrome marbles. The bowed frontal is in a purplish-red marble, and incorporates a design feature like an ancient bath-tub. Yellow Siena and green verde antico marbles are used in bands above and below this, as well as to the sides of the aedicule above, and below the altarpiece is a band of alabaster. All this polychromy, especially the deep red, focuses attention on the sculptures which are in white marble and so stand out.