In architecture, a coffer is a sunken panel on a ceiling or dome that has both structural and ornamental purposes. Structurally, it lightens the ceiling as less concrete or other materials are needed for its construction. Coffers were a common feature of Roman architecture, as exemplified by those forming the dome of the Pantheon in Rome. Renaissance architects revived the use of coffers in the 15th century, among them Leon Battista Alberti who coffered the barrel vault over the nave of Sant'Andrea, Mantua (beg. 1470), to direct the viewer's eyes to the altar. Other examples include the entrance vestibule in the Palazzo Farnese, Rome (c. 1513-1589), built by Antonio da Sangallo the Younger, where the barrel vault is coffered, and the entrance to the Oratory of St. Philip Neri, Rome (1637-1656), by Francesco Borromini, which is contained in a coffered niche in perspective.
Historical dictionary of Renaissance art. Lilian H. Zirpolo. 2008.