In the next two decades della Robbia executed important commissions in marble and bronze: a series of marble reliefs (1437) for the bell tower of the Cathedral of Florence; a marble and enameled terra-cotta tabernacle (1443), now in S. Maria in Peretola; bronze angels to enrich the Singing Gallery; and, in collaboration with Michelozzo, the large project of bronze doors for the Sacristy of the Cathedral. These doors were not finished until 1469; their reliance on a few figures placed in simple, orderly compositions against a flat ground, contrasts sharply with the elaborate pictorial effects of Lorenzo Ghiberti's more famous Baptistery doors.