This paper reports on acoustical measurements made with Vatican permission in several large churches, including St. Peter's Basilica and the other three Patriarchal Basilicas in Rome: S. Giovanni in Laterano, S. Paolo fuori le Mura, and S. Maria Maggiore. The observed reverberation times for these large churches are unusually short. This is because of the acoustical coupling of the air volumes making up the structures and also the profusion of architectural detail and decoration, especially sculpture, that produces a very considerable amount of sound diffusion. The measured reverberation times are consistent with standard reverberation theory when the coupled nature of the air volumes is considered.